diff --git a/gcc/cp/lex.c b/gcc/cp/lex.c
index c83346b617d..73e14b8394c 100644
--- a/gcc/cp/lex.c
+++ b/gcc/cp/lex.c
@@ -515,7 +515,7 @@ struct module_token_filter
 	  {
 	  module_end:;
 	    /* End of the directive, handle the name.  */
-	    if (import)
+	    if (import && (is_import || !flag_header_unit))
 	      if (module_state *m
 		  = preprocess_module (import, token_loc, module != NULL,
 				       is_import, got_export, reader))
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 378e4572f8b..f636bb746d4 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -13745,7 +13745,13 @@ cp_parser_module_declaration (cp_parser *parser, module_parse mp_state,
   parser->lexer->in_pragma = true;
   cp_token *token = cp_lexer_consume_token (parser->lexer);
 
-  if (mp_state == MP_FIRST && !exporting
+  if (flag_header_unit)
+    {
+      error_at (token->location,
+		"module-declaration not permitted in header-unit");
+      goto skip_eol;
+    }
+  else if (mp_state == MP_FIRST && !exporting
       && cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON))
     {
       /* Start global module fragment.  */
diff --git a/gcc/testsuite/g++.dg/modules/pr99468.H b/gcc/testsuite/g++.dg/modules/pr99468.H
new file mode 100644
index 00000000000..b6be0c349d5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr99468.H
@@ -0,0 +1,7 @@
+// PR 99468, stupidly worded diagnostic
+// { dg-additional-options -fmodule-header }
+
+module M; // { dg-error "module-declaration not permitted" }
+
+int i;
+// { dg-prune-output "not writing" }