diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 5704511..de7b980 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1429,6 +1429,27 @@
         'defcompile'], 'E1003:')
   delfunc! g:Func
 
+  CheckScriptFailure([
+        'def Func():number',
+        'return 123',
+        'enddef',
+        'defcompile'], 'E1069:')
+  delfunc! g:Func
+
+  CheckScriptFailure([
+        'def Func() :number',
+        'return 123',
+        'enddef',
+        'defcompile'], 'E1059:')
+  delfunc! g:Func
+
+  CheckScriptFailure([
+        'def Func() : number',
+        'return 123',
+        'enddef',
+        'defcompile'], 'E1059:')
+  delfunc! g:Func
+
   CheckScriptFailure(['def Func(): list', 'return []', 'enddef'], 'E1008:')
   delfunc! g:Func
   CheckScriptFailure(['def Func(): dict', 'return {}', 'enddef'], 'E1008:')
diff --git a/src/userfunc.c b/src/userfunc.c
index 79a6621..7a7617f 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -4066,8 +4066,15 @@
     if (eap->cmdidx == CMD_def)
     {
 	// find the return type: :def Func(): type
-	if (*p == ':')
+	if (*skipwhite(p) == ':')
 	{
+	    if (*p != ':')
+	    {
+		semsg(_(e_no_white_space_allowed_before_colon_str), p);
+		p = skipwhite(p);
+	    }
+	    else if (!IS_WHITE_OR_NUL(p[1]))
+		semsg(_(e_white_space_required_after_str_str), ":", p);
 	    ret_type = skipwhite(p + 1);
 	    p = skip_type(ret_type, FALSE);
 	    if (p > ret_type)
diff --git a/src/version.c b/src/version.c
index 3e209fe..aacefc0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3317,
+/**/
     3316,
 /**/
     3315,