Fix minor grammar typo.
diff --git a/Python/ceval.c b/Python/ceval.c
index 1f18545..2a0a57c 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2772,7 +2772,7 @@
 				}
 				PyErr_Format(PyExc_TypeError,
 					"%.200s() needs "
-					"keyword only argument %s",
+					"keyword-only argument %s",
 					PyString_AsString(co->co_name),
 					PyString_AsString(name));
 				goto fail;