diff -r 1c486516b39e Modules/_datetimemodule.c
--- a/Modules/_datetimemodule.c	Thu Dec 29 23:57:31 2016 -0700
+++ b/Modules/_datetimemodule.c	Fri Dec 30 05:54:55 2016 -0500
@@ -4269,7 +4269,21 @@
      */
     second = Py_MIN(59, tm.tm_sec);
 
-    if (tzinfo == Py_None && f == _PyTime_localtime) {
+    /* On Windows, passing a negative value to local results
+    * in an OSError because localtime_s on Windows does
+    * not support negative timestamps. Unfortunately this
+    * means that fold detection for time values between
+    * 0 and max_fold_seconds will result in an identical
+    * error since we subtract max_fold_seconds to detect a
+    * fold. However, since we know there haven't been any
+    * folds in the interval [0, max_fold_seconds) in any
+    * timezone, we can hackily just forego fold detection
+    * for this time range on Windows. */
+    if (tzinfo == Py_None && f == _PyTime_localtime
+#ifdef MS_WINDOWS
+        && (timet - max_fold_seconds > 0)
+#endif
+        ) {
         long long probe_seconds, result_seconds, transition;
 
         result_seconds = utc_to_seconds(year, month, day,