diff --git a/internal/re/regexp.go b/internal/re/regexp.go
index cf978d5..dad5079 100644
--- a/internal/re/regexp.go
+++ b/internal/re/regexp.go
@@ -211,6 +211,9 @@ func (this *Regexp) parseKeyword(keyword []rune) (result []rune) {
 			}
 			if keyword[index-1] != '\\' {
 				if r == '{' && (braceZero.MatchString(string(keyword[index:])) || braceZero2.MatchString(string(keyword[index:]))) { // r {0, ...}
+					if len(result) == 0 {
+						return nil
+					}
 					return result[:len(result)-1]
 				}
 
@@ -221,6 +224,9 @@ func (this *Regexp) parseKeyword(keyword []rune) (result []rune) {
 			if index == 0 {
 				return nil
 			}
+			if len(result) == 0 {
+				return nil
+			}
 			return result[:len(result)-1]
 		}
 		if r == '\\' || r == '\b' {