diff --git a/pwrapis/src/utils.c b/pwrapis/src/utils.c
index 483f863073d0436c96c614108ba14cd937e9924b..5a47c74a9e2a6ecb638241e1b7ea70434d368139 100644
--- a/pwrapis/src/utils.c
+++ b/pwrapis/src/utils.c
@@ -784,7 +784,7 @@ void LRtrim(char *str)
     while (isspace(str[head])) {
         head++;
     }
-    while (isspace(str[tail])) {
+    while (tail>=0&&isspace(str[tail])) {
         tail--;
     }
     int i;