diff --git a/src/guid/ntapi_tt_guid.c b/src/guid/ntapi_tt_guid.c
index 52eb5af..69a5926 100644
--- a/src/guid/ntapi_tt_guid.c
+++ b/src/guid/ntapi_tt_guid.c
@@ -107,13 +107,25 @@ int32_t __fastcall __ntapi_tt_string_to_guid_utf16(
 	wchar16_t *	wch;
 	uint16_t	key;
 
-	if ((guid_str->lbrace != '{')
-			|| (guid_str->rbrace != '}')
-			|| (guid_str->dash1 != '-')
+	/* outer braces / outer underscores / outer dashes */
+	if ((guid_str->lbrace == '{') && (guid_str->rbrace == '}'))
+		(void)0;
+
+	else if ((guid_str->lbrace == '_') && (guid_str->rbrace == '_'))
+		(void)0;
+
+	else if ((guid_str->lbrace == '-') && (guid_str->rbrace == '-'))
+		(void)0;
+
+	else
+		return NT_STATUS_INVALID_PARAMETER;
+
+	/* inner dashes */
+	if ((guid_str->dash1 != '-')
 			|| (guid_str->dash2 != '-')
 			|| (guid_str->dash3 != '-')
 			|| (guid_str->dash4 != '-'))
-			return NT_STATUS_INVALID_PARAMETER;
+		return NT_STATUS_INVALID_PARAMETER;
 
 	wch = &(guid_str->group5[0]);