diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 85fd8ff..1ccaeb3 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -131,6 +131,8 @@
   CheckDefFailure(['def Nested(arg: string)', 'enddef', 'Nested()'], 'E119:')
 
   CheckDefFailure(['func Nested()', 'endfunc'], 'E1086:')
+  CheckDefFailure(['def s:Nested()', 'enddef'], 'E1075:')
+  CheckDefFailure(['def b:Nested()', 'enddef'], 'E1075:')
 enddef
 
 func Test_call_default_args_from_func()
diff --git a/src/version.c b/src/version.c
index 00d8c2d..f032581 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1351,
+/**/
     1350,
 /**/
     1349,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 6581708..61be54d 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -4899,12 +4899,18 @@
 {
     int		is_global = *eap->arg == 'g' && eap->arg[1] == ':';
     char_u	*name_start = eap->arg;
-    char_u	*name_end = to_name_end(eap->arg, is_global);
+    char_u	*name_end = to_name_end(eap->arg, TRUE);
     char_u	*lambda_name;
     lvar_T	*lvar;
     ufunc_T	*ufunc;
     int		r;
 
+    // Only g:Func() can use a namespace.
+    if (name_start[1] == ':' && !is_global)
+    {
+	semsg(_(e_namespace), name_start);
+	return NULL;
+    }
     if (check_defined(name_start, name_end - name_start, cctx) == FAIL)
 	return NULL;