diff --git a/manifests/iface.pp b/manifests/iface.pp
index 006831b..7575921 100644
--- a/manifests/iface.pp
+++ b/manifests/iface.pp
@@ -2,21 +2,21 @@
   case $family {
     inet: {
       if ! ($method in [loopback, static, manual, dhcp, bootp, ppp, wvdial]) {
-        fail('$method parameter must be one of loopback, static, manual, dhcp, bootp, ppp or wvdial for $family inet')
+        fail('method parameter must be one of loopback, static, manual, dhcp, bootp, ppp or wvdial for family inet')
       }
     }
     inet6: {
       if ! ($method in [loopback, static, manual, v4tunnel]) {
-        fail('$method parameter must be one of loopback, static, manual or v4tunnel for $family inet6')
+        fail('method parameter must be one of loopback, static, manual or v4tunnel for family inet6')
       }
     }
     ipx: {
       if ! ($method in [static, dynamic]) {
-        fail('$method parameter must be static or dynamic for $family ipx')
+        fail('method parameter must be static or dynamic for family ipx')
       }
     }
     default: {
-      fail('$family parameter must be one of inet, inet6 or ipx')
+      fail('family parameter must be one of inet, inet6 or ipx')
     }
   }
 
diff --git a/spec/defines/iface_spec.rb b/spec/defines/iface_spec.rb
index c239b13..ddc03c2 100644
--- a/spec/defines/iface_spec.rb
+++ b/spec/defines/iface_spec.rb
@@ -13,6 +13,17 @@
 
 describe 'interfaces::iface' do
   let(:title) { 'eth0' }
+  let(:params) { { :family => 'inet', :method => 'dhcp' } }
+
+  it {
+    should_not contain_interfaces__auto('eth0')
+    should contain_concat__fragment('interfaces::iface_eth0').with_target('/etc/network/interfaces')
+    should contain_concat__fragment('interfaces::iface_eth0').with_content("iface eth0 inet dhcp\n\t\n\n")
+  }
+end
+
+describe 'interfaces::iface' do
+  let(:title) { 'eth0' }
   let(:params) { { :family => 'inet', :method => 'dhcp', :auto => 1 } }
 
   it {
@@ -65,3 +76,47 @@
     should contain_concat__fragment('interfaces::iface_eth0v6').with_content("iface eth0 inet6 static\n\taddress 2001:db8::1\n\tnetmask 64\n\n")
   }
 end
+
+describe 'interfaces::iface' do
+  let(:title) { 'eth0' }
+  let(:params) { { :ifname => 'eth0', :family => 'foobar', :method => 'foobar' } }
+
+  it {
+    expect {
+      should contain_concat__fragment('interfaces::iface_eth0').with_target('/etc/network/interfaces')
+    }.to raise_error(Puppet::Error, /family parameter must be one of inet, inet6 or ipx/)
+  }
+end
+
+describe 'interfaces::iface' do
+  let(:title) { 'eth0' }
+  let(:params) { { :ifname => 'eth0', :family => 'inet6', :method => 'foobar' } }
+
+  it {
+    expect {
+      should contain_concat__fragment('interfaces::iface_eth0').with_target('/etc/network/interfaces')
+    }.to raise_error(Puppet::Error, /method parameter must be one of loopback, static, manual or v4tunnel for family inet6/)
+  }
+end
+
+describe 'interfaces::iface' do
+  let(:title) { 'eth0' }
+  let(:params) { { :ifname => 'eth0', :family => 'ipx', :method => 'foobar' } }
+
+  it {
+    expect {
+      should contain_concat__fragment('interfaces::iface_eth0').with_target('/etc/network/interfaces')
+    }.to raise_error(Puppet::Error, /method parameter must be static or dynamic for family ipx/)
+  }
+end
+
+describe 'interfaces::iface' do
+  let(:title) { 'eth0' }
+  let(:params) { { :ifname => 'eth0', :family => 'inet', :method => 'foobar' } }
+
+  it {
+    expect {
+      should contain_concat__fragment('interfaces::iface_eth0').with_target('/etc/network/interfaces')
+    }.to raise_error(Puppet::Error, /method parameter must be one of loopback, static, manual, dhcp, bootp, ppp or wvdial for family inet/)
+  }
+end