diff --git a/var/spack/repos/builtin/packages/py-cython/package.py b/var/spack/repos/builtin/packages/py-cython/package.py
index b348d561e2a..c75e151c1a4 100644
--- a/var/spack/repos/builtin/packages/py-cython/package.py
+++ b/var/spack/repos/builtin/packages/py-cython/package.py
@@ -43,4 +43,4 @@ def command(self):
 
     def test(self):
         # Warning: full suite of unit tests takes a very long time
-        python('runtests.py', '-j', make_jobs)
+        python('runtests.py', '-j', str(make_jobs))