diff --git a/lib/component_factory.rb b/lib/component_factory.rb
index 60567a8..17da3ae 100644
--- a/lib/component_factory.rb
+++ b/lib/component_factory.rb
@@ -18,7 +18,7 @@ def _pass_through_attributes(elem)
   end
 
   def _has_class(elem, klass)
-    (elem.attr('class') || '').include?(klass)
+    elem.attr('class') =~ /(^|\s)#{klass}($|\s)/
   end
 
   def _combine_classes(elem, extra_classes)
diff --git a/spec/cases/button/with_tricky_class.inky b/spec/cases/button/with_tricky_class.inky
index b8adefc..3f4d2da 100644
--- a/spec/cases/button/with_tricky_class.inky
+++ b/spec/cases/button/with_tricky_class.inky
@@ -1,5 +1,19 @@
-<!-- pending -->
-
 <button href="http://example.com" class="noexpand">
   A label
 </button>
+
+<button href="http://example.com" class="expand-niet">
+  A label
+</button>
+
+<button href="http://example.com" class="expand foo">
+  A label
+</button>
+
+<button href="http://example.com" class="foo expand">
+  A label
+</button>
+
+<button href="http://example.com" class="foo expand bar">
+  A label
+</button>