diff --git a/extra/calendar/calendar.factor b/extra/calendar/calendar.factor
index 32c5c0233c..012080d3b7 100755
--- a/extra/calendar/calendar.factor
+++ b/extra/calendar/calendar.factor
@@ -349,17 +349,23 @@ M: timestamp year. ( timestamp -- )
 : timestamp>string ( timestamp -- str )
     [ (timestamp>string) ] string-out ;
 
+: (write-gmt-offset) ( ratio -- )
+    1 /mod swap write-00 60 * write-00 ;
+
+: write-gmt-offset ( gmt-offset -- )
+    {
+        { [ dup zero? ] [ drop "GMT" write ] }
+        { [ dup 0 < ] [ "-" write neg (write-gmt-offset) ] }
+        { [ dup 0 > ] [ "+" write (write-gmt-offset) ] }
+    } cond ;
+
 : timestamp>rfc822-string ( timestamp -- str )
     #! RFC822 timestamp format
     #! Example: Tue, 15 Nov 1994 08:12:31 +0200
     [
         dup (timestamp>string)
         " " write
-        timestamp-gmt-offset {
-            { [ dup zero? ] [ drop "GMT" write ] }
-            { [ dup 0 < ] [ "-" write neg write-00 "00" write ] }
-            { [ dup 0 > ] [ "+" write write-00 "00" write ] }
-        } cond
+        timestamp-gmt-offset write-gmt-offset
     ] string-out ;
 
 : timestamp>http-string ( timestamp -- str )
diff --git a/extra/calendar/windows/windows.factor b/extra/calendar/windows/windows.factor
index 320400822c..9e34fdac00 100755
--- a/extra/calendar/windows/windows.factor
+++ b/extra/calendar/windows/windows.factor
@@ -6,8 +6,10 @@ TUPLE: windows-calendar ;
 
 T{ windows-calendar } calendar-backend set-global
 
+: TIME_ZONE_ID_INVALID HEX: ffffffff ; inline
+
 M: windows-calendar gmt-offset ( -- float )
     "TIME_ZONE_INFORMATION" <c-object>
-    [ GetTimeZoneInformation win32-error=0/f ] keep
-    [ TIME_ZONE_INFORMATION-Bias ] keep
-    TIME_ZONE_INFORMATION-DaylightBias + 60 /f neg ;
+    dup GetTimeZoneInformation
+    TIME_ZONE_ID_INVALID = [ win32-error ] when
+    TIME_ZONE_INFORMATION-Bias 60 / neg ;