diff --git a/lib/WebGUI/Shop/ShipDriver.pm b/lib/WebGUI/Shop/ShipDriver.pm
index f0fd09518..1b4cadc58 100644
--- a/lib/WebGUI/Shop/ShipDriver.pm
+++ b/lib/WebGUI/Shop/ShipDriver.pm
@@ -60,6 +60,19 @@ sub _buildObj {
 }
 
 
+#-------------------------------------------------------------------
+
+=head2 calculate (  )
+
+This method calculates how much it costs to ship the contents of a cart.  This method
+MUST be overridden in all child classes.
+
+=cut
+
+sub calculate {
+    croak "You must override the calculate method";
+}
+
 #-------------------------------------------------------------------
 
 =head2 className (  )
diff --git a/t/Shop/ShipDriver.t b/t/Shop/ShipDriver.t
index a7a0db5db..8cc66638c 100644
--- a/t/Shop/ShipDriver.t
+++ b/t/Shop/ShipDriver.t
@@ -31,7 +31,7 @@ my $session         = WebGUI::Test->session;
 #----------------------------------------------------------------------------
 # Tests
 
-my $tests = 28;
+my $tests = 29;
 plan tests => 1 + $tests;
 
 #----------------------------------------------------------------------------
@@ -238,6 +238,15 @@ is($driver->getId,           $driverCopy->getId,     'same id');
 is($driver->className,       $driverCopy->className, 'same className');
 cmp_deeply($driver->options, $driverCopy->options,   'same options');
 
+#######################################################################
+#
+# calculate
+#
+#######################################################################
+
+eval { $driver->calculate; };
+like ($@, qr/^You must override the calculate method/, 'calculate throws an exception to force overriding it in the child classes');
+
 #######################################################################
 #
 # delete
@@ -251,12 +260,6 @@ is($count, 0, 'delete deleted the object');
 
 undef $driver;
 
-#######################################################################
-#
-# calculate
-#
-#######################################################################
-
 }
 
 #----------------------------------------------------------------------------