diff --git a/index.js b/index.js
index d9f237d..9061056 100644
--- a/index.js
+++ b/index.js
@@ -147,6 +147,10 @@ function tzset (tz) {
   debug('set the current timezone to:', usedTz);
   if (!rtn.tzname[1] && rtn.timezone === 0) {
     debug('got bad zoneinfo object:', rtn);
+    if (tz !== exports.currentTimezone) {
+      // restore original timezone in case of error
+      tzset(exports.currentTimezone);
+    }
     var err = new Error("Unknown Timezone: '" + usedTz + "'");
     for (var i in rtn) {
       err[i] = rtn[i];
diff --git a/test/date.js b/test/date.js
index 92be017..585d187 100644
--- a/test/date.js
+++ b/test/date.js
@@ -51,6 +51,13 @@ describe('Date', function () {
       initial.should.equal(process.env.TZ)
     })
 
+    it('should clean up after an error', function () {
+      var initial = process.env.TZ
+        , d = new time.Date
+      d.setTimezone.bind(d, 'Any/Wrong/TZ').should.throw(/^Unknown Timezone/)
+      initial.should.equal(process.env.TZ)
+    })
+
     it('should change the "timezone offset"', function () {
       var d = new time.Date
         , offset = d.getTimezoneOffset()