diff --git a/clang/lib/Sema/SemaModule.cpp b/clang/lib/Sema/SemaModule.cpp
--- a/clang/lib/Sema/SemaModule.cpp
+++ b/clang/lib/Sema/SemaModule.cpp
@@ -395,7 +395,7 @@
     // [module.interface]p1:
     // An export-declaration shall inhabit a namespace scope and appear in the
     // purview of a module interface unit.
-    Diag(ExportLoc, diag::err_export_not_in_module_interface);
+    Diag(ExportLoc, diag::err_export_not_in_module_interface) << 0;
   }
 
   return Import;
diff --git a/clang/test/Modules/cxx20-export-import.cpp b/clang/test/Modules/cxx20-export-import.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/cxx20-export-import.cpp
@@ -0,0 +1,3 @@
+
+// RUN: %clang_cc1 -std=c++20 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -verify %s
+export import dummy; // expected-error {{export declaration can only be used within a module interface unit after the module declaration}}