diff -r a3bdbe220f8a Lib/multiprocessing/spawn.py
--- a/Lib/multiprocessing/spawn.py	Tue Dec 10 14:06:18 2013 +0200
+++ b/Lib/multiprocessing/spawn.py	Wed Dec 11 10:50:29 2013 +0100
@@ -232,6 +232,7 @@
         # contain additional code that should still be executed
         import importlib
         import types
+        import imp
 
         if main_path is None:
             dirs = None
@@ -248,6 +249,15 @@
         main_module = types.ModuleType(main_name)
         # XXX Use a target of main_module?
         spec = importlib.find_spec(main_name, path=dirs)
+        if spec is None:
+            # This can happen for source scripts that do not have the '.py'
+            # extension under POSIX system. Force loading the module from the
+            # source file in that case
+            imp.load_source(main_name, main_path)
+            spec = importlib.find_spec(main_name, path=dirs)
+        if spec is None:
+            raise RuntimeError("Failed to load main module %s from %s"
+                               % (main_name, main_path))
         methods = importlib._bootstrap._SpecMethods(spec)
         methods.init_module_attrs(main_module)
         main_module.__name__ = '__mp_main__'