diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -32,7 +32,10 @@ class changelog(revlog):
     def add(self, manifest, list, desc, transaction, p1=None, p2=None,
                   user=None, date=None):
         if date:
-            when, offset = map(int, date.split())
+            # validate explicit (probably user-specified) date and
+            # time zone offset
+            when, offset = map(int, date.split(' '))
+            time.localtime(when)
             assert abs(offset) < 43200, 'bad time zone offset: %d' % offset
         else:
             if time.daylight: offset = time.altzone