diff --git a/src/harness/collections.ts b/src/harness/collections.ts
index 7c71296409c98..aa0eae6731791 100644
--- a/src/harness/collections.ts
+++ b/src/harness/collections.ts
@@ -245,7 +245,7 @@ namespace collections {
     export class Metadata {
         private static readonly _undefinedValue = {};
         private _parent: Metadata | undefined;
-        private _map: { [key: string]: any };
+        private _map!: { [key: string]: any };
         private _version = 0;
         private _size = -1;
         private _parentVersion: number | undefined;
diff --git a/src/harness/fakes.ts b/src/harness/fakes.ts
index 093f57a112b81..5354187631769 100644
--- a/src/harness/fakes.ts
+++ b/src/harness/fakes.ts
@@ -207,7 +207,7 @@ namespace fakes {
      */
     export class CompilerHost implements ts.CompilerHost {
         public readonly sys: System;
-        public readonly defaultLibLocation: string;
+        public readonly defaultLibLocation!: string;
         public readonly outputs: documents.TextDocument[] = [];
         private readonly _outputsMap: collections.SortedMap<string, number>;
         public readonly traces: string[] = [];