diff --git a/gunicorn/util.py b/gunicorn/util.py
index e919d53c..d0e56425 100644
--- a/gunicorn/util.py
+++ b/gunicorn/util.py
@@ -146,6 +146,9 @@ def set_owner_process(uid,gid):
             # groups like on osx or fedora
             os.setgid(-ctypes.c_int(-gid).value)
 
+        # Also drop supplemental groups
+        os.setgroups([])
+
     if uid:
         os.setuid(uid)