diff --git a/lib/et-orbi/time.rb b/lib/et-orbi/time.rb
index cf531e9..9dc00dc 100644
--- a/lib/et-orbi/time.rb
+++ b/lib/et-orbi/time.rb
@@ -110,8 +110,11 @@ def seconds=(f)
 
     def zone=(z)
 
+      tz = self.class.get_tzone(z || zone)
+      fail ArgumentError.new("Cannot determine timezone from #{z.inspect}") \
+        unless tz
 
-      @zone = self.class.get_tzone(zone || :current)
+      @zone = tz
 
       touch
 
diff --git a/test/eo_time_test.rb b/test/eo_time_test.rb
index c9fc480..f53f9e0 100644
--- a/test/eo_time_test.rb
+++ b/test/eo_time_test.rb
@@ -113,6 +113,33 @@
     end
   end
 
+  group '#zone=' do
+
+    test 'assigns the requested timezone and invalidates the time cache' do
+
+      ot = EtOrbi::EoTime.new(0, 'UTC')
+      ot.hour
+
+      ot.zone = 'Asia/Kolkata'
+
+      assert ot.zone.name, 'Asia/Kolkata'
+      assert ot.hour, 5
+      assert ot.min, 30
+      assert ot.to_f, 0.0
+    end
+
+    test 'does not change the timezone when assignment fails' do
+
+      ot = EtOrbi::EoTime.new(0, 'UTC')
+
+      assert_error(
+        lambda { ot.zone = 'Invalid/Timezone' },
+        ArgumentError)
+
+      assert ot.zone.name, 'UTC'
+    end
+  end
+
   group '.utc' do
 
     [