--- tor-0.2.0.30/src/common/compat.c.setgroups
+++ tor-0.2.0.30/src/common/compat.c
@@ -897,6 +897,11 @@ switch_id(const char *user, const char *
       return -1;
     }
 
+    if (getgroups(0,0)!=0 && setgroups(0,0)!=0) {
+      log_warn(LD_GENERAL,"Error setting groups: %s", strerror(errno));
+      return -1;
+    }
+
     if (setgid(gr->gr_gid) != 0) {
       log_warn(LD_GENERAL,"Error setting to configured GID: %s",
                strerror(errno));