Index: setup.py
--- setup.py.orig
+++ setup.py
@@ -339,7 +339,7 @@ except ImportError:
 try:
     if force_cython:
         log.info("Updating C extension with Cython.")
-        subprocess.check_call(["cython", "shapely/speedups/_speedups.pyx"])
+        subprocess.check_call(["cython${MODPY_BIN_SUFFIX}", "shapely/speedups/_speedups.pyx"])
 except (subprocess.CalledProcessError, OSError):
     log.warning("Could not (re)create C extension with Cython.")
     if force_cython: