diff --git a/IPython/extensions/tests/test_cythonmagic.py b/IPython/extensions/tests/test_cythonmagic.py
index af3aa8d..91e3a5f 100644
--- a/IPython/extensions/tests/test_cythonmagic.py
+++ b/IPython/extensions/tests/test_cythonmagic.py
@@ -34,6 +34,9 @@ def test_cython_pyximport():
     ip.run_cell_magic('cython_pyximport', module_name, code)
     ip.ex('g = f(10)')
     nt.assert_equal(ip.user_ns['g'], 20.0)
+    ip.run_cell_magic('cython_pyximport', module_name, code)
+    ip.ex('h = f(-10)')
+    nt.assert_equal(ip.user_ns['h'], -20.0)
     try:
         os.remove(module_name+'.pyx')
     except OSError: