diff --git a/bin/diamond b/bin/diamond
index f59e7d41f..1a09dcf78 100755
--- a/bin/diamond
+++ b/bin/diamond
@@ -204,11 +204,13 @@ def main():
 
                     # Python 2.7+
                     if hasattr(os, 'initgroups'):
-                        os.initgroups(user, gid)
+                        os.initgroups(pwd.getpwuid(uid).pw_name, gid)
                     # Python 2.6
                     else:
-                        os.setgroups([e.gr_gid for e in grp.getgrall()
-                                      if user in e.gr_mem] + [gid])
+                        os.setgroups(
+                            [e.gr_gid for e in grp.getgrall() if pwd.getpwuid(
+                                uid).pw_name in e.gr_mem] + [gid]
+                            )
 
                 if gid != -1 and os.getgid() != gid:
                     # Set GID
@@ -333,6 +335,7 @@ def main():
         log.error("traceback: %s" % traceback.format_exc())
         sys.exit(1)
 
+
 if __name__ == "__main__":
     if setproctitle:
         setproctitle(os.path.basename(__file__))