diff --git a/source3/lib/substitute.c b/source3/lib/substitute.c
index 08cc03e..2d59b59 100644
--- a/source3/lib/substitute.c
+++ b/source3/lib/substitute.c
@@ -606,7 +606,8 @@ char *talloc_sub_specified(TALLOC_CTX *mem_ctx,
 			const char *username,
 			const char *domain,
 			uid_t uid,
-			gid_t gid)
+			gid_t gid;
+			const char *grpname)
 {
 	char *a_string;
 	char *ret_string = NULL;
@@ -639,9 +640,14 @@ char *talloc_sub_specified(TALLOC_CTX *mem_ctx,
 			break;
 		case 'G' :
 			if (gid != -1) {
-				a_string = talloc_string_sub(
-					tmp_ctx, a_string, "%G",
-					gidtoname(gid));
+				if (grpname == NULL)
+					a_string = talloc_string_sub(
+						tmp_ctx, a_string, "%G",
+						gidtoname(gid));
+				else
+					a_string = talloc_string_sub(
+						tmp_ctx, a_string, "%G",
+						grpname);
 			} else {
 				a_string = talloc_string_sub(
 					tmp_ctx, a_string,
@@ -650,9 +656,14 @@ char *talloc_sub_specified(TALLOC_CTX *mem_ctx,
 			break;
 		case 'g' :
 			if (gid != -1) {
-				a_string = talloc_string_sub(
-					tmp_ctx, a_string, "%g",
-					gidtoname(gid));
+				if (grpname == NULL)
+					a_string = talloc_string_sub(
+						tmp_ctx, a_string, "%g",
+						gidtoname(gid));
+				else
+					a_string = talloc_string_sub(
+						tmp_ctx, a_string, "%g",
+						grpname);
 			} else {
 				a_string = talloc_string_sub(
 					tmp_ctx, a_string, "%g", "NO_GROUP");