diff --git a/php/ext/google/protobuf/names.c b/php/ext/google/protobuf/names.c
index 212aded35b..87ac40de76 100644
--- a/php/ext/google/protobuf/names.c
+++ b/php/ext/google/protobuf/names.c
@@ -285,8 +285,10 @@ bool IsPreviouslyUnreservedClassName(const char* fullname) {
   int j;
   for (j = 0; kPreviouslyUnreservedNames[j]; j++) {
     if (strcmp(kPreviouslyUnreservedNames[j], lower) == 0) {
+      free(lower);
       return true;
     }
   }
+  free(lower);
   return false;
 }