diff -u b/conditional_fields.module b/conditional_fields.module
--- b/conditional_fields.module
+++ b/conditional_fields.module
@@ -541,13 +541,10 @@
       }
 
       // Add validation callback to element if the dependency can be evaluated.
-      if (in_array($options['condition'], array('value', 'empty', '!empty'))) {
+      if (in_array($options['condition'], array('value', 'empty', '!empty', 'checked', '!checked'))) {
         _conditional_fields_element_add_property($dependent_form_field, '#element_validate', 'conditional_fields_dependent_validate', 'append');
       }
 
-      // Add validation callback to element.
-      _conditional_fields_element_add_property($dependent_form_field, '#element_validate', 'conditional_fields_dependent_validate', 'append');
-
       // Add the $state into the correct logic group in $states.
       foreach ($state as $key => $constraints) {
         foreach ($constraints as $selector => $constraint) {
@@ -1044,7 +1041,7 @@
 
   foreach ($dependencies as $dependency_id => $dependency) {
     // Skip dependencies that can't be evaluated.
-    if (!in_array($dependency['options']['condition'], array('value', 'empty', '!empty'))) {
+    if (!in_array($dependency['options']['condition'], array('value', 'empty', '!empty', 'checked', '!checked'))) {
       continue;
     }