diff --git a/src/model/immutable/ContentBlock.js b/src/model/immutable/ContentBlock.js
index 32ba9f1b15..c0034b6be9 100644
--- a/src/model/immutable/ContentBlock.js
+++ b/src/model/immutable/ContentBlock.js
@@ -26,7 +26,7 @@ const {List, Map, OrderedSet, Record, Repeat} = Immutable;
 const EMPTY_SET = OrderedSet();
 
 type ContentBlockConfig = {
-  key?: string,
+  key?: DraftBlockType,
   type?: string,
   text?: string,
   characterList?: List<CharacterMetadata>,