diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 6948829..2d065cf 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -411,6 +411,7 @@
 		if (bimod == NULL ||
 		    PyDict_SetItemString(d, "__builtins__", bimod) != 0)
 			Py_FatalError("can't add __builtins__ to __main__");
+		Py_DECREF(bimod);
 	}
 }