diff --git a/lib/WebGUI/Shop/Tax.pm b/lib/WebGUI/Shop/Tax.pm
index ef660a73b..020922305 100644
--- a/lib/WebGUI/Shop/Tax.pm
+++ b/lib/WebGUI/Shop/Tax.pm
@@ -37,7 +37,8 @@ Add tax information to the table.  Returns the taxId of the newly created tax in
 
 =head3 $params
 
-A hash ref of the geographic and rate information.  All parameters are required.
+A hash ref of the geographic and rate information.  All parameters are required and
+must have defined values.
 
 =head4 field
 
@@ -62,6 +63,12 @@ sub add {
     my $self   = shift;
     my $params = shift;
     my $id = $self->session->id->generate();
+    croak "Must pass in a hashref"
+        unless ref($params) eq 'HASH';
+    foreach my $key (qw/field value taxRate/) {
+        croak "Hash ref must contain a $key key with a defined value"
+            unless exists($params->{$key}) and defined $params->{$key};
+    }
     $self->session->db->write('insert into tax (taxId, field, value, taxRate) VALUES (?,?,?,?)', [$id, @{ $params }{qw[ field value taxRate ]}]);
     return $id;
 }
diff --git a/t/Shop/Tax.t b/t/Shop/Tax.t
index d2824be4e..f351b0f81 100644
--- a/t/Shop/Tax.t
+++ b/t/Shop/Tax.t
@@ -28,7 +28,7 @@ my $session         = WebGUI::Test->session;
 #----------------------------------------------------------------------------
 # Tests
 
-my $tests = 17;
+my $tests = 24;
 plan tests => 1 + $tests;
 
 #----------------------------------------------------------------------------
@@ -72,6 +72,46 @@ is($taxIterator->rows, 0, 'WebGUI ships with no predefined tax data');
 #
 #######################################################################
 
+eval{$taxer->add()};
+like($@, qr{Must pass in a hashref},
+    'add: error handling for missing hashref');
+
+eval{$taxer->add({})};
+like($@, qr{Hash ref must contain a field key with a defined value},
+    'add: error handling for missing field hashref key');
+
+my $taxData = {
+    field   => undef,
+};
+
+eval{$taxer->add($taxData)};
+like($@, qr{Hash ref must contain a field key with a defined value},
+    'add: error handling for undefined field key');
+
+$taxData->{field} = 'state';
+
+eval{$taxer->add($taxData)};
+like($@, qr{Hash ref must contain a value key with a defined value},
+    'add: error handling for missing value key');
+
+$taxData->{value} = undef;
+
+eval{$taxer->add($taxData)};
+like($@, qr{Hash ref must contain a value key with a defined value},
+    'add: error handling for undefined value key');
+
+$taxData->{value} = 'Oregon';
+
+eval{$taxer->add($taxData)};
+like($@, qr{Hash ref must contain a taxRate key with a defined value},
+    'add: error handling for missing taxRate key');
+
+$taxData->{taxRate} = undef;
+
+eval{$taxer->add($taxData)};
+like($@, qr{Hash ref must contain a taxRate key with a defined value},
+    'add: error handling for undefined taxRate key');
+
 my $taxData = {
     field   => 'state',
     value   => 'Oregon',