diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index bbe6930..9ce0928 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -13438,6 +13438,9 @@
   if (Mod->getTopLevelModuleName() == getLangOpts().CurrentModule)
     Diag(ImportLoc, diag::err_module_self_import)
         << Mod->getFullModuleName() << getLangOpts().CurrentModule;
+  else if (Mod->getTopLevelModuleName() == getLangOpts().ImplementationOfModule)
+    Diag(ImportLoc, diag::err_module_import_in_implementation)
+        << Mod->getFullModuleName() << getLangOpts().ImplementationOfModule;
 
   SmallVector<SourceLocation, 2> IdentifierLocs;
   Module *ModCheck = Mod;