diff --git a/Python/ceval.c b/Python/ceval.c
index 60a91b2..037c86c 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1617,6 +1617,8 @@
 							"lost sys.stdout");
 			}
 			if (w != NULL) {
+				/* w.write() may replace sys.stdout, so we
+				 * have to keep our reference to it */
 				Py_INCREF(w);
 				err = PyFile_WriteString("\n", w);
 				if (err == 0)