diff --git a/src/sign.c b/src/sign.c
index 66a29db..2c102e4 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -1078,13 +1078,28 @@
 	return FAIL;
 
     if (linehl != NULL)
-	sp->sn_line_hl = syn_check_group(linehl, (int)STRLEN(linehl));
+    {
+	if (*linehl == NUL)
+	    sp->sn_line_hl = 0;
+	else
+	    sp->sn_line_hl = syn_check_group(linehl, (int)STRLEN(linehl));
+    }
 
     if (texthl != NULL)
-	sp->sn_text_hl = syn_check_group(texthl, (int)STRLEN(texthl));
+    {
+	if (*texthl == NUL)
+	    sp->sn_text_hl = 0;
+	else
+	    sp->sn_text_hl = syn_check_group(texthl, (int)STRLEN(texthl));
+    }
 
     if (culhl != NULL)
-	sp->sn_cul_hl = syn_check_group(culhl, (int)STRLEN(culhl));
+    {
+	if (*culhl == NUL)
+	    sp->sn_cul_hl = 0;
+	else
+	    sp->sn_cul_hl = syn_check_group(culhl, (int)STRLEN(culhl));
+    }
 
     return OK;
 }
@@ -1319,7 +1334,11 @@
     char_u	*linehl = NULL;
     char_u	*texthl = NULL;
     char_u	*culhl = NULL;
-    int failed = FALSE;
+    int		failed = FALSE;
+    sign_T	*sp_prev;
+    int		exists;
+
+    exists = sign_find(sign_name, &sp_prev) != NULL;
 
     // set values for a defined sign.
     for (;;)
@@ -1341,7 +1360,7 @@
 	else if (STRNCMP(arg, "linehl=", 7) == 0)
 	{
 	    arg += 7;
-	    if (check_empty_group(p - arg, "linehl") == FAIL)
+	    if (!exists && check_empty_group(p - arg, "linehl") == FAIL)
 	    {
 		failed = TRUE;
 		break;
@@ -1351,7 +1370,7 @@
 	else if (STRNCMP(arg, "texthl=", 7) == 0)
 	{
 	    arg += 7;
-	    if (check_empty_group(p - arg, "texthl") == FAIL)
+	    if (!exists && check_empty_group(p - arg, "texthl") == FAIL)
 	    {
 		failed = TRUE;
 		break;
@@ -1361,7 +1380,7 @@
 	else if (STRNCMP(arg, "culhl=", 6) == 0)
 	{
 	    arg += 6;
-	    if (check_empty_group(p - arg, "culhl") == FAIL)
+	    if (!exists && check_empty_group(p - arg, "culhl") == FAIL)
 	    {
 		failed = TRUE;
 		break;