diff --git a/toolchain/check/BUILD b/toolchain/check/BUILD
index bfeefba008bdc..4d2dcada5584d 100644
--- a/toolchain/check/BUILD
+++ b/toolchain/check/BUILD
@@ -131,6 +131,7 @@ cc_library(
         "//toolchain/lex:tokenized_buffer",
         "//toolchain/parse:node_kind",
         "//toolchain/parse:tree",
+        "//toolchain/sem_ir:clang_decl",
         "//toolchain/sem_ir:expr_info",
         "//toolchain/sem_ir:file",
         "//toolchain/sem_ir:formatter",
diff --git a/toolchain/check/import_cpp.cpp b/toolchain/check/import_cpp.cpp
index a26320aee3461..8142d9454d96a 100644
--- a/toolchain/check/import_cpp.cpp
+++ b/toolchain/check/import_cpp.cpp
@@ -38,6 +38,7 @@
 #include "toolchain/diagnostics/diagnostic_emitter.h"
 #include "toolchain/diagnostics/format_providers.h"
 #include "toolchain/parse/node_ids.h"
+#include "toolchain/sem_ir/clang_decl.h"
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/name_scope.h"
 #include "toolchain/sem_ir/typed_insts.h"
@@ -462,8 +463,21 @@ static auto ClangLookup(Context& context, SemIR::NameScopeId scope_id,
   return lookup;
 }
 
+// If `decl` already mapped to an instruction, returns that instruction.
+// Otherwise returns `None`.
+static auto LookupClangDeclInstId(Context& context, clang::Decl* decl)
+    -> SemIR::InstId {
+  auto& clang_decls = context.sem_ir().clang_decls();
+  if (auto context_clang_decl_id = clang_decls.Lookup(decl);
+      context_clang_decl_id.has_value()) {
+    return clang_decls.Get(context_clang_decl_id).inst_id;
+  }
+  return SemIR::InstId::None;
+}
+
 // Imports a namespace declaration from Clang to Carbon. If successful, returns
-// the new Carbon namespace declaration `InstId`.
+// the new Carbon namespace declaration `InstId`. If the declaration was already
+// imported, returns the mapped instruction.
 static auto ImportNamespaceDecl(Context& context,
                                 SemIR::NameScopeId parent_scope_id,
                                 SemIR::NameId name_id,
@@ -484,15 +498,17 @@ static auto AsCarbonNamespace(Context& context,
                               clang::DeclContext* decl_context)
     -> SemIR::InstId {
   CARBON_CHECK(decl_context);
-  auto& clang_decls = context.sem_ir().clang_decls();
-
-  // Check if the decl context is already mapped to a Carbon namespace.
-  if (auto context_clang_decl_id =
-          clang_decls.Lookup(clang::dyn_cast<clang::Decl>(decl_context));
-      context_clang_decl_id.has_value()) {
-    return clang_decls.Get(context_clang_decl_id).inst_id;
+  // Check if the declaration is already mapped.
+  // TODO: Try to avoid this check by rotating the loops below so they treat the
+  // given decl_context the same at its enclosing contexts.
+  if (SemIR::InstId existing_inst_id = LookupClangDeclInstId(
+          context, clang::dyn_cast<clang::Decl>(decl_context));
+      existing_inst_id.has_value()) {
+    return existing_inst_id;
   }
 
+  auto& clang_decls = context.sem_ir().clang_decls();
+
   // We know we have at least one context to map, add all decl contexts we need
   // to map.
   llvm::SmallVector<clang::DeclContext*> decl_contexts;
@@ -681,12 +697,9 @@ static auto MapRecordType(Context& context, SemIR::LocId loc_id,
     return {.inst_id = SemIR::TypeInstId::None, .type_id = SemIR::TypeId::None};
   }
 
-  auto& clang_decls = context.sem_ir().clang_decls();
-  SemIR::InstId record_inst_id = SemIR::InstId::None;
-  if (auto record_clang_decl_id = clang_decls.Lookup(record_decl);
-      record_clang_decl_id.has_value()) {
-    record_inst_id = clang_decls.Get(record_clang_decl_id).inst_id;
-  } else {
+  // Check if the declaration is already mapped.
+  SemIR::InstId record_inst_id = LookupClangDeclInstId(context, record_decl);
+  if (!record_inst_id.has_value()) {
     auto parent_inst_id =
         AsCarbonNamespace(context, record_decl->getDeclContext());
     auto parent_name_scope_id =
@@ -1041,12 +1054,20 @@ static auto CreateFunctionParamsInsts(Context& context, SemIR::LocId loc_id,
 }
 
 // Imports a function declaration from Clang to Carbon. If successful, returns
-// the new Carbon function declaration `InstId`.
+// the new Carbon function declaration `InstId`. If the declaration was already
+// imported, returns the mapped instruction.
 static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
                                SemIR::NameScopeId scope_id,
                                SemIR::NameId name_id,
                                clang::FunctionDecl* clang_decl)
     -> SemIR::InstId {
+  // Check if the declaration is already mapped.
+  if (SemIR::InstId existing_inst_id =
+          LookupClangDeclInstId(context, clang_decl);
+      existing_inst_id.has_value()) {
+    return existing_inst_id;
+  }
+
   if (clang_decl->isVariadic()) {
     context.TODO(loc_id, "Unsupported: Variadic function");
     MarkFailedDecl(context, clang_decl);
@@ -1114,6 +1135,9 @@ static auto ImportFunctionDecl(Context& context, SemIR::LocId loc_id,
 }
 // Imports a declaration from Clang to Carbon. If successful, returns the
 // instruction for the new Carbon declaration.
+// TODO: Remove `scope_id` parameter since we the scope the name was found in
+// isn't necessarily the parent scope. See
+// https://github.com/carbon-language/carbon-lang/pull/5789/files/a5629ebb303c5b1aef46181eb860b7065ca1aaf1#r2201769611
 static auto ImportNameDecl(Context& context, SemIR::LocId loc_id,
                            SemIR::NameScopeId scope_id, SemIR::NameId name_id,
                            clang::NamedDecl* clang_decl) -> SemIR::InstId {
@@ -1123,8 +1147,8 @@ static auto ImportNameDecl(Context& context, SemIR::LocId loc_id,
   }
   if (auto* clang_namespace_decl =
           clang::dyn_cast<clang::NamespaceDecl>(clang_decl)) {
-    return ImportNamespaceDecl(context, scope_id, name_id,
-                               clang_namespace_decl);
+    return AsCarbonNamespace(
+        context, llvm::dyn_cast<clang::DeclContext>(clang_namespace_decl));
   }
   if (auto* type_decl = clang::dyn_cast<clang::TypeDecl>(clang_decl)) {
     auto type = type_decl->getASTContext().getTypeDeclType(type_decl);
diff --git a/toolchain/check/testdata/interop/cpp/class/class.carbon b/toolchain/check/testdata/interop/cpp/class/class.carbon
index f9f9356df5ad2..6df643967f68b 100644
--- a/toolchain/check/testdata/interop/cpp/class/class.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/class.carbon
@@ -576,11 +576,9 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
 // CHECK:STDOUT:   %Bar1: type = class_type @Bar1 [concrete]
-// CHECK:STDOUT:   %foo1.type.148: type = fn_type @foo1.1 [concrete]
-// CHECK:STDOUT:   %foo1.8cd: %foo1.type.148 = struct_value () [concrete]
+// CHECK:STDOUT:   %foo1.type: type = fn_type @foo1 [concrete]
+// CHECK:STDOUT:   %foo1: %foo1.type = struct_value () [concrete]
 // CHECK:STDOUT:   %Bar2: type = class_type @Bar2 [concrete]
-// CHECK:STDOUT:   %foo1.type.0b8: type = fn_type @foo1.2 [concrete]
-// CHECK:STDOUT:   %foo1.ba2: %foo1.type.0b8 = struct_value () [concrete]
 // CHECK:STDOUT:   %foo2.type: type = fn_type @foo2 [concrete]
 // CHECK:STDOUT:   %foo2: %foo2.type = struct_value () [concrete]
 // CHECK:STDOUT: }
@@ -592,9 +590,8 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Bar1.decl: type = class_decl @Bar1 [concrete = constants.%Bar1] {} {}
-// CHECK:STDOUT:   %foo1.decl.c80: %foo1.type.148 = fn_decl @foo1.1 [concrete = constants.%foo1.8cd] {} {}
+// CHECK:STDOUT:   %foo1.decl: %foo1.type = fn_decl @foo1 [concrete = constants.%foo1] {} {}
 // CHECK:STDOUT:   %Bar2.decl: type = class_decl @Bar2 [concrete = constants.%Bar2] {} {}
-// CHECK:STDOUT:   %foo1.decl.191: %foo1.type.0b8 = fn_decl @foo1.2 [concrete = constants.%foo1.ba2] {} {}
 // CHECK:STDOUT:   %foo2.decl: %foo2.type = fn_decl @foo2 [concrete = constants.%foo2] {} {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -603,12 +600,12 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:   %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT:   %Bar1.ref: type = name_ref Bar1, imports.%Bar1.decl [concrete = constants.%Bar1]
-// CHECK:STDOUT:   %foo1.ref.loc8: %foo1.type.148 = name_ref foo1, imports.%foo1.decl.c80 [concrete = constants.%foo1.8cd]
+// CHECK:STDOUT:   %foo1.ref.loc8: %foo1.type = name_ref foo1, imports.%foo1.decl [concrete = constants.%foo1]
 // CHECK:STDOUT:   %foo1.call.loc8: init %empty_tuple.type = call %foo1.ref.loc8()
 // CHECK:STDOUT:   %Cpp.ref.loc9: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT:   %Bar2.ref.loc9: type = name_ref Bar2, imports.%Bar2.decl [concrete = constants.%Bar2]
-// CHECK:STDOUT:   %foo1.ref.loc9: %foo1.type.0b8 = name_ref foo1, imports.%foo1.decl.191 [concrete = constants.%foo1.ba2]
+// CHECK:STDOUT:   %foo1.ref.loc9: %foo1.type = name_ref foo1, imports.%foo1.decl [concrete = constants.%foo1]
 // CHECK:STDOUT:   %foo1.call.loc9: init %empty_tuple.type = call %foo1.ref.loc9()
 // CHECK:STDOUT:   %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   %Bar2.ref.loc10: type = name_ref Bar2, imports.%Bar2.decl [concrete = constants.%Bar2]
diff --git a/toolchain/check/testdata/interop/cpp/class/struct.carbon b/toolchain/check/testdata/interop/cpp/class/struct.carbon
index a8d7b78ad5d99..b92cb399d2dfb 100644
--- a/toolchain/check/testdata/interop/cpp/class/struct.carbon
+++ b/toolchain/check/testdata/interop/cpp/class/struct.carbon
@@ -567,11 +567,9 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
 // CHECK:STDOUT:   %Bar1: type = class_type @Bar1 [concrete]
-// CHECK:STDOUT:   %foo1.type.148: type = fn_type @foo1.1 [concrete]
-// CHECK:STDOUT:   %foo1.8cd: %foo1.type.148 = struct_value () [concrete]
+// CHECK:STDOUT:   %foo1.type: type = fn_type @foo1 [concrete]
+// CHECK:STDOUT:   %foo1: %foo1.type = struct_value () [concrete]
 // CHECK:STDOUT:   %Bar2: type = class_type @Bar2 [concrete]
-// CHECK:STDOUT:   %foo1.type.0b8: type = fn_type @foo1.2 [concrete]
-// CHECK:STDOUT:   %foo1.ba2: %foo1.type.0b8 = struct_value () [concrete]
 // CHECK:STDOUT:   %foo2.type: type = fn_type @foo2 [concrete]
 // CHECK:STDOUT:   %foo2: %foo2.type = struct_value () [concrete]
 // CHECK:STDOUT: }
@@ -583,9 +581,8 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:   %Bar1.decl: type = class_decl @Bar1 [concrete = constants.%Bar1] {} {}
-// CHECK:STDOUT:   %foo1.decl.c80: %foo1.type.148 = fn_decl @foo1.1 [concrete = constants.%foo1.8cd] {} {}
+// CHECK:STDOUT:   %foo1.decl: %foo1.type = fn_decl @foo1 [concrete = constants.%foo1] {} {}
 // CHECK:STDOUT:   %Bar2.decl: type = class_decl @Bar2 [concrete = constants.%Bar2] {} {}
-// CHECK:STDOUT:   %foo1.decl.191: %foo1.type.0b8 = fn_decl @foo1.2 [concrete = constants.%foo1.ba2] {} {}
 // CHECK:STDOUT:   %foo2.decl: %foo2.type = fn_decl @foo2 [concrete = constants.%foo2] {} {}
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
@@ -594,12 +591,12 @@ fn MyF(bar: Cpp.Bar*);
 // CHECK:STDOUT:   %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT:   %Bar1.ref: type = name_ref Bar1, imports.%Bar1.decl [concrete = constants.%Bar1]
-// CHECK:STDOUT:   %foo1.ref.loc8: %foo1.type.148 = name_ref foo1, imports.%foo1.decl.c80 [concrete = constants.%foo1.8cd]
+// CHECK:STDOUT:   %foo1.ref.loc8: %foo1.type = name_ref foo1, imports.%foo1.decl [concrete = constants.%foo1]
 // CHECK:STDOUT:   %foo1.call.loc8: init %empty_tuple.type = call %foo1.ref.loc8()
 // CHECK:STDOUT:   %Cpp.ref.loc9: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT:   %Bar2.ref.loc9: type = name_ref Bar2, imports.%Bar2.decl [concrete = constants.%Bar2]
-// CHECK:STDOUT:   %foo1.ref.loc9: %foo1.type.0b8 = name_ref foo1, imports.%foo1.decl.191 [concrete = constants.%foo1.ba2]
+// CHECK:STDOUT:   %foo1.ref.loc9: %foo1.type = name_ref foo1, imports.%foo1.decl [concrete = constants.%foo1]
 // CHECK:STDOUT:   %foo1.call.loc9: init %empty_tuple.type = call %foo1.ref.loc9()
 // CHECK:STDOUT:   %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   %Bar2.ref.loc10: type = name_ref Bar2, imports.%Bar2.decl [concrete = constants.%Bar2]
diff --git a/toolchain/check/testdata/interop/cpp/function/class.carbon b/toolchain/check/testdata/interop/cpp/function/class.carbon
index 612642b51be51..c76b7e680f5d1 100644
--- a/toolchain/check/testdata/interop/cpp/function/class.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/class.carbon
@@ -183,6 +183,8 @@ import Cpp library "definition_in_namespace_value_param_type.h";
 fn F() {
   //@dump-sem-ir-begin
   Cpp.foo({});
+  // Check that the parameter type was imported correctly.
+  var x: Cpp.N.C;
   //@dump-sem-ir-end
 }
 
@@ -539,6 +541,7 @@ fn F() {
 // CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
 // CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
+// CHECK:STDOUT:   %pattern_type.69f: type = pattern_type %C [concrete]
 // CHECK:STDOUT:   %foo.type: type = fn_type @foo [concrete]
 // CHECK:STDOUT:   %foo: %foo.type = struct_value () [concrete]
 // CHECK:STDOUT:   %C.val: %C = struct_value () [concrete]
@@ -550,8 +553,14 @@ fn F() {
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
 // CHECK:STDOUT:     .foo = %foo.decl
+// CHECK:STDOUT:     .N = %N
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
+// CHECK:STDOUT:   %N: <namespace> = namespace [concrete] {
+// CHECK:STDOUT:     .C = %C.decl
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %C.decl: type = class_decl @C [concrete = constants.%C] {} {}
 // CHECK:STDOUT:   %foo.decl: %foo.type = fn_decl @foo [concrete = constants.%foo] {
 // CHECK:STDOUT:     <elided>
 // CHECK:STDOUT:   } {
@@ -561,7 +570,7 @@ fn F() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F() {
 // CHECK:STDOUT: !entry:
-// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   %foo.ref: %foo.type = name_ref foo, imports.%foo.decl [concrete = constants.%foo]
 // CHECK:STDOUT:   %.loc8_12.1: %empty_struct_type = struct_literal ()
 // CHECK:STDOUT:   %.loc8_12.2: ref %C = temporary_storage
@@ -570,11 +579,27 @@ fn F() {
 // CHECK:STDOUT:   %.loc8_12.5: ref %C = converted %.loc8_12.1, %.loc8_12.4
 // CHECK:STDOUT:   %.loc8_12.6: %C = bind_value %.loc8_12.5
 // CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call %foo.ref(%.loc8_12.6)
-// CHECK:STDOUT:   %Op.bound: <bound method> = bound_method %.loc8_12.2, constants.%Op.dbb
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %x.patt: %pattern_type.69f = binding_pattern x [concrete]
+// CHECK:STDOUT:     %x.var_patt: %pattern_type.69f = var_pattern %x.patt [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %x.var: ref %C = var %x.var_patt
+// CHECK:STDOUT:   %.loc10: type = splice_block %C.ref [concrete = constants.%C] {
+// CHECK:STDOUT:     %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:     %N.ref: <namespace> = name_ref N, imports.%N [concrete = imports.%N]
+// CHECK:STDOUT:     %C.ref: type = name_ref C, imports.%C.decl [concrete = constants.%C]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %x: ref %C = bind_name x, %x.var
+// CHECK:STDOUT:   %Op.bound.loc10: <bound method> = bound_method %x.var, constants.%Op.dbb
 // CHECK:STDOUT:   <elided>
-// CHECK:STDOUT:   %bound_method: <bound method> = bound_method %.loc8_12.2, %Op.specific_fn
-// CHECK:STDOUT:   %addr: %ptr.838 = addr_of %.loc8_12.2
-// CHECK:STDOUT:   %no_op: init %empty_tuple.type = call %bound_method(%addr)
+// CHECK:STDOUT:   %bound_method.loc10: <bound method> = bound_method %x.var, %Op.specific_fn.1
+// CHECK:STDOUT:   %addr.loc10: %ptr.838 = addr_of %x.var
+// CHECK:STDOUT:   %no_op.loc10: init %empty_tuple.type = call %bound_method.loc10(%addr.loc10)
+// CHECK:STDOUT:   %Op.bound.loc8: <bound method> = bound_method %.loc8_12.2, constants.%Op.dbb
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %bound_method.loc8: <bound method> = bound_method %.loc8_12.2, %Op.specific_fn.2
+// CHECK:STDOUT:   %addr.loc8: %ptr.838 = addr_of %.loc8_12.2
+// CHECK:STDOUT:   %no_op.loc8: init %empty_tuple.type = call %bound_method.loc8(%addr.loc8)
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/interop/cpp/function/struct.carbon b/toolchain/check/testdata/interop/cpp/function/struct.carbon
index f82bf8d6e5cd3..9b0a9bde7a085 100644
--- a/toolchain/check/testdata/interop/cpp/function/struct.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/struct.carbon
@@ -183,6 +183,8 @@ import Cpp library "definition_in_namespace_value_param_type.h";
 fn F() {
   //@dump-sem-ir-begin
   Cpp.foo({});
+  // Check that the parameter type was imported correctly.
+  var x: Cpp.N.S;
   //@dump-sem-ir-end
 }
 
@@ -539,6 +541,7 @@ fn F() {
 // CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
 // CHECK:STDOUT:   %S: type = class_type @S [concrete]
 // CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
+// CHECK:STDOUT:   %pattern_type.cd8: type = pattern_type %S [concrete]
 // CHECK:STDOUT:   %foo.type: type = fn_type @foo [concrete]
 // CHECK:STDOUT:   %foo: %foo.type = struct_value () [concrete]
 // CHECK:STDOUT:   %S.val: %S = struct_value () [concrete]
@@ -550,8 +553,14 @@ fn F() {
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
 // CHECK:STDOUT:     .foo = %foo.decl
+// CHECK:STDOUT:     .N = %N
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
+// CHECK:STDOUT:   %N: <namespace> = namespace [concrete] {
+// CHECK:STDOUT:     .S = %S.decl
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %S.decl: type = class_decl @S [concrete = constants.%S] {} {}
 // CHECK:STDOUT:   %foo.decl: %foo.type = fn_decl @foo [concrete = constants.%foo] {
 // CHECK:STDOUT:     <elided>
 // CHECK:STDOUT:   } {
@@ -561,7 +570,7 @@ fn F() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F() {
 // CHECK:STDOUT: !entry:
-// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   %foo.ref: %foo.type = name_ref foo, imports.%foo.decl [concrete = constants.%foo]
 // CHECK:STDOUT:   %.loc8_12.1: %empty_struct_type = struct_literal ()
 // CHECK:STDOUT:   %.loc8_12.2: ref %S = temporary_storage
@@ -570,11 +579,27 @@ fn F() {
 // CHECK:STDOUT:   %.loc8_12.5: ref %S = converted %.loc8_12.1, %.loc8_12.4
 // CHECK:STDOUT:   %.loc8_12.6: %S = bind_value %.loc8_12.5
 // CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call %foo.ref(%.loc8_12.6)
-// CHECK:STDOUT:   %Op.bound: <bound method> = bound_method %.loc8_12.2, constants.%Op.9b3
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %x.patt: %pattern_type.cd8 = binding_pattern x [concrete]
+// CHECK:STDOUT:     %x.var_patt: %pattern_type.cd8 = var_pattern %x.patt [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %x.var: ref %S = var %x.var_patt
+// CHECK:STDOUT:   %.loc10: type = splice_block %S.ref [concrete = constants.%S] {
+// CHECK:STDOUT:     %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:     %N.ref: <namespace> = name_ref N, imports.%N [concrete = imports.%N]
+// CHECK:STDOUT:     %S.ref: type = name_ref S, imports.%S.decl [concrete = constants.%S]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %x: ref %S = bind_name x, %x.var
+// CHECK:STDOUT:   %Op.bound.loc10: <bound method> = bound_method %x.var, constants.%Op.9b3
 // CHECK:STDOUT:   <elided>
-// CHECK:STDOUT:   %bound_method: <bound method> = bound_method %.loc8_12.2, %Op.specific_fn
-// CHECK:STDOUT:   %addr: %ptr.edf = addr_of %.loc8_12.2
-// CHECK:STDOUT:   %no_op: init %empty_tuple.type = call %bound_method(%addr)
+// CHECK:STDOUT:   %bound_method.loc10: <bound method> = bound_method %x.var, %Op.specific_fn.1
+// CHECK:STDOUT:   %addr.loc10: %ptr.edf = addr_of %x.var
+// CHECK:STDOUT:   %no_op.loc10: init %empty_tuple.type = call %bound_method.loc10(%addr.loc10)
+// CHECK:STDOUT:   %Op.bound.loc8: <bound method> = bound_method %.loc8_12.2, constants.%Op.9b3
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %bound_method.loc8: <bound method> = bound_method %.loc8_12.2, %Op.specific_fn.2
+// CHECK:STDOUT:   %addr.loc8: %ptr.edf = addr_of %.loc8_12.2
+// CHECK:STDOUT:   %no_op.loc8: init %empty_tuple.type = call %bound_method.loc8(%addr.loc8)
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/interop/cpp/function/union.carbon b/toolchain/check/testdata/interop/cpp/function/union.carbon
index b4127ed6f772d..8eca37d7049d3 100644
--- a/toolchain/check/testdata/interop/cpp/function/union.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/union.carbon
@@ -199,6 +199,8 @@ import Cpp library "definition_in_namespace_value_param_type.h";
 fn F() {
   //@dump-sem-ir-begin
   Cpp.foo({});
+  // Check that the parameter type was imported correctly.
+  var x: Cpp.N.U;
   //@dump-sem-ir-end
 }
 
@@ -555,6 +557,7 @@ fn F() {
 // CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
 // CHECK:STDOUT:   %U: type = class_type @U [concrete]
 // CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
+// CHECK:STDOUT:   %pattern_type.eb9: type = pattern_type %U [concrete]
 // CHECK:STDOUT:   %foo.type: type = fn_type @foo [concrete]
 // CHECK:STDOUT:   %foo: %foo.type = struct_value () [concrete]
 // CHECK:STDOUT:   %U.val: %U = struct_value () [concrete]
@@ -566,8 +569,14 @@ fn F() {
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
 // CHECK:STDOUT:     .foo = %foo.decl
+// CHECK:STDOUT:     .N = %N
 // CHECK:STDOUT:     import Cpp//...
 // CHECK:STDOUT:   }
+// CHECK:STDOUT:   %N: <namespace> = namespace [concrete] {
+// CHECK:STDOUT:     .U = %U.decl
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %U.decl: type = class_decl @U [concrete = constants.%U] {} {}
 // CHECK:STDOUT:   %foo.decl: %foo.type = fn_decl @foo [concrete = constants.%foo] {
 // CHECK:STDOUT:     <elided>
 // CHECK:STDOUT:   } {
@@ -577,7 +586,7 @@ fn F() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F() {
 // CHECK:STDOUT: !entry:
-// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
 // CHECK:STDOUT:   %foo.ref: %foo.type = name_ref foo, imports.%foo.decl [concrete = constants.%foo]
 // CHECK:STDOUT:   %.loc8_12.1: %empty_struct_type = struct_literal ()
 // CHECK:STDOUT:   %.loc8_12.2: ref %U = temporary_storage
@@ -586,11 +595,27 @@ fn F() {
 // CHECK:STDOUT:   %.loc8_12.5: ref %U = converted %.loc8_12.1, %.loc8_12.4
 // CHECK:STDOUT:   %.loc8_12.6: %U = bind_value %.loc8_12.5
 // CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call %foo.ref(%.loc8_12.6)
-// CHECK:STDOUT:   %Op.bound: <bound method> = bound_method %.loc8_12.2, constants.%Op.d5d
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %x.patt: %pattern_type.eb9 = binding_pattern x [concrete]
+// CHECK:STDOUT:     %x.var_patt: %pattern_type.eb9 = var_pattern %x.patt [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %x.var: ref %U = var %x.var_patt
+// CHECK:STDOUT:   %.loc10: type = splice_block %U.ref [concrete = constants.%U] {
+// CHECK:STDOUT:     %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:     %N.ref: <namespace> = name_ref N, imports.%N [concrete = imports.%N]
+// CHECK:STDOUT:     %U.ref: type = name_ref U, imports.%U.decl [concrete = constants.%U]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %x: ref %U = bind_name x, %x.var
+// CHECK:STDOUT:   %Op.bound.loc10: <bound method> = bound_method %x.var, constants.%Op.d5d
 // CHECK:STDOUT:   <elided>
-// CHECK:STDOUT:   %bound_method: <bound method> = bound_method %.loc8_12.2, %Op.specific_fn
-// CHECK:STDOUT:   %addr: %ptr.87e = addr_of %.loc8_12.2
-// CHECK:STDOUT:   %no_op: init %empty_tuple.type = call %bound_method(%addr)
+// CHECK:STDOUT:   %bound_method.loc10: <bound method> = bound_method %x.var, %Op.specific_fn.1
+// CHECK:STDOUT:   %addr.loc10: %ptr.87e = addr_of %x.var
+// CHECK:STDOUT:   %no_op.loc10: init %empty_tuple.type = call %bound_method.loc10(%addr.loc10)
+// CHECK:STDOUT:   %Op.bound.loc8: <bound method> = bound_method %.loc8_12.2, constants.%Op.d5d
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %bound_method.loc8: <bound method> = bound_method %.loc8_12.2, %Op.specific_fn.2
+// CHECK:STDOUT:   %addr.loc8: %ptr.87e = addr_of %.loc8_12.2
+// CHECK:STDOUT:   %no_op.loc8: init %empty_tuple.type = call %bound_method.loc8(%addr.loc8)
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT: }
 // CHECK:STDOUT: