Index: clang/lib/Sema/SemaModule.cpp
===================================================================
--- clang/lib/Sema/SemaModule.cpp
+++ clang/lib/Sema/SemaModule.cpp
@@ -576,7 +576,8 @@
 
   CurContext->addDecl(D);
   PushDeclContext(S, D);
-  D->setModuleOwnershipKind(Decl::ModuleOwnershipKind::VisibleWhenImported);
+  if (getCurrentModule() && getCurrentModule()->isModulePurview())
+    D->setModuleOwnershipKind(Decl::ModuleOwnershipKind::VisibleWhenImported);
   return D;
 }
 
Index: clang/test/Modules/export-in-non-modules.cpp
===================================================================
--- /dev/null
+++ clang/test/Modules/export-in-non-modules.cpp
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -std=c++20 %s -fsyntax-only -verify
+export struct Unit { // expected-error {{export declaration can only be used within a module interface unit after the module declaration}}
+    bool operator<(const Unit&);
+};