diff --git a/src/server/client.ts b/src/server/client.ts
index ea6c948c4fb..864dac9fdaa 100644
--- a/src/server/client.ts
+++ b/src/server/client.ts
@@ -537,6 +537,7 @@ namespace ts.server {
                     fileName,
                     textSpan: ts.createTextSpanFromBounds(start, end),
                     isWriteAccess: entry.isWriteAccess,
+                    isDefinition: false
                 };
             });
         }
diff --git a/src/server/protocol.d.ts b/src/server/protocol.d.ts
index dd29411f97d..b62d89ae520 100644
--- a/src/server/protocol.d.ts
+++ b/src/server/protocol.d.ts
@@ -308,7 +308,7 @@ declare namespace ts.server.protocol {
         /**
          * True if reference is a definition, false otherwise.
          */
-        isDefinition?: boolean;
+        isDefinition: boolean;
     }
 
     /**
diff --git a/src/services/services.ts b/src/services/services.ts
index 5e1b69170a5..4f5bdbdc469 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1208,7 +1208,7 @@ namespace ts {
         textSpan: TextSpan;
         fileName: string;
         isWriteAccess: boolean;
-        isDefinition?: boolean;
+        isDefinition: boolean;
     }
 
     export interface DocumentHighlights {
@@ -5750,7 +5750,8 @@ namespace ts {
                         result.push({
                             fileName: entry.fileName,
                             textSpan: highlightSpan.textSpan,
-                            isWriteAccess: highlightSpan.kind === HighlightSpanKind.writtenReference
+                            isWriteAccess: highlightSpan.kind === HighlightSpanKind.writtenReference,
+                            isDefinition: false
                         });
                     }
                 }