diff --git a/py/magic/greenlet.py b/py/magic/greenlet.py
index 90d46b134..b35c3074a 100644
--- a/py/magic/greenlet.py
+++ b/py/magic/greenlet.py
@@ -2,8 +2,10 @@ import sys
 if '_stackless' in sys.builtin_module_names:
     # when running on top of a pypy with stackless support
     from _stackless import greenlet
+elif hasattr(sys, 'pypy_objspaceclass'):
+    raise ImportError("Detected pypy without stackless support")
 else:
-    # regular CPython (or pypy without stackless support, and then crash :-)
+    # regular CPython
     import py
     gdir = py.path.local(py.__file__).dirpath() 
     path = gdir.join('c-extension', 'greenlet', 'greenlet.c')