Index: clang/lib/Sema/SemaModule.cpp
===================================================================
--- clang/lib/Sema/SemaModule.cpp
+++ clang/lib/Sema/SemaModule.cpp
@@ -615,12 +615,10 @@
   return llvm::None;
 }
 
-unsigned getUnnamedDeclDiag(UnnamedDeclKind UDK, bool InBlock) {
+static unsigned getUnnamedDeclDiag(UnnamedDeclKind UDK, bool InBlock) {
   switch (UDK) {
   case UnnamedDeclKind::Empty:
   case UnnamedDeclKind::StaticAssert:
-    // Allow empty-declarations and static_asserts in an export block as an
-    // extension.
     return InBlock ? diag::ext_export_no_name_block : diag::err_export_no_name;
 
   case UnnamedDeclKind::UsingDirective:
@@ -648,10 +646,19 @@
 
 /// Check that it's valid to export \p D.
 static bool checkExportedDecl(Sema &S, Decl *D, SourceLocation BlockStart) {
-  // C++2a [module.interface]p3:
-  //   An exported declaration shall declare at least one name
-  if (auto UDK = getUnnamedDeclKind(D))
-    diagExportedUnnamedDecl(S, *UDK, D, BlockStart);
+  if (auto UDK = getUnnamedDeclKind(D)) {
+    if (S.getLangOpts().CPlusPlus2b) {
+      // P1766R1 allows unnamed declarations in export{} blocks, but not in
+      // the single-declaration form of export.
+      // FIXME: Cite the standard once P1766R1 is reflected in the wording
+      if (BlockStart.isInvalid())
+        diagExportedUnnamedDecl(S, *UDK, D, BlockStart);
+    } else {
+      // C++2a [module.interface]p3:
+      //   An exported declaration shall declare at least one name
+      diagExportedUnnamedDecl(S, *UDK, D, BlockStart);
+    }
+  }
 
   //   [...] shall not declare a name with internal linkage.
   if (auto *ND = dyn_cast<NamedDecl>(D)) {
Index: clang/test/Modules/cxx20-export.cpp
===================================================================
--- /dev/null
+++ clang/test/Modules/cxx20-export.cpp
@@ -0,0 +1,23 @@
+
+// RUN: %clang_cc1 -std=c++2b -verify %s
+export module testmodule;
+
+export static_assert(true); // expected-error {{static_assert declaration cannot be exported}}
+export;                     // expected-error {{empty declaration cannot be exported}}
+
+namespace A {};
+
+export {
+#define STR(x) constexpr char x[] = #x;
+  STR(foo);
+#undef STR
+
+  static_assert(true);
+
+  template <typename T> struct X { T t; };
+  template <typename T> X(T) -> X<T>;
+
+  ; // Empty declaration
+
+  using namespace A;
+}