diff --git a/flag.flag.inc b/flag.flag.inc
index c7ff2ecb7bea9aba66577b7650356cede64b8792..242ab776cddf9b8adc7ddd9acbc874766eb9271a 100644
--- a/flag.flag.inc
+++ b/flag.flag.inc
@@ -62,6 +62,13 @@ function flag_flag_type_info_alter(&$definitions) {
     // Only add flag support for entities that don't yet have them, and which
     // are non-config entities.
     if (!isset($definitions[$entity_type]) && empty($entity_info['configuration'])) {
+      // We deliberately exclude taxonomy vocabularies from the list of
+      // supported entity types because they aren't fieldable or directly
+      // viewable, which makes them impossible to flag.
+      if ($entity_type === 'taxonomy_vocabulary') {
+        continue;
+      }
+
       $definitions[$entity_type] = array(
         'title' => $entity_info['label'],
         'description' => t('@entity-type entity', array('@entity-type' => $entity_info['label'])),