diff --git a/code/lib/instrumenter/src/instrumenter.test.ts b/code/lib/instrumenter/src/instrumenter.test.ts
index c15d5516fd1c..da65f5498dd7 100644
--- a/code/lib/instrumenter/src/instrumenter.test.ts
+++ b/code/lib/instrumenter/src/instrumenter.test.ts
@@ -29,6 +29,7 @@ class HTMLElement {
   }
 }
 
+// @ts-expect-error (global scope type conflicts)
 delete global.location;
 // @ts-expect-error (global scope type conflicts)
 global.location = { reload: jest.fn() };
diff --git a/code/lib/instrumenter/src/instrumenter.ts b/code/lib/instrumenter/src/instrumenter.ts
index 0d8c2c9ddc78..357b9df52817 100644
--- a/code/lib/instrumenter/src/instrumenter.ts
+++ b/code/lib/instrumenter/src/instrumenter.ts
@@ -40,8 +40,10 @@ const alreadyCompletedException = new Error(
   `This function ran after the play function completed. Did you forget to \`await\` it?`
 );
 
-const isObject = (o: unknown) => Object.prototype.toString.call(o) === '[object Object]';
-const isModule = (o: unknown) => Object.prototype.toString.call(o) === '[object Module]';
+const isObject = (o: unknown): o is object =>
+  Object.prototype.toString.call(o) === '[object Object]';
+const isModule = (o: unknown): o is NodeModule =>
+  Object.prototype.toString.call(o) === '[object Module]';
 const isInstrumentable = (o: unknown) => {
   if (!isObject(o) && !isModule(o)) return false;
   if (o.constructor === undefined) return true;
@@ -108,7 +110,7 @@ export class Instrumenter {
       isPlaying = true,
       isDebugging = false,
     }: {
-      storyId?: StoryId;
+      storyId: StoryId;
       isPlaying?: boolean;
       isDebugging?: boolean;
     }) => {
@@ -575,8 +577,8 @@ export class Instrumenter {
         return;
       }
 
-      const hasPrevious = logItems.some((item) =>
-        [CallStates.DONE, CallStates.ERROR].includes(item.status)
+      const hasPrevious = logItems.some(
+        (item) => item.status === CallStates.DONE || item.status === CallStates.ERROR
       );
       const controlStates: ControlStates = {
         start: hasPrevious,
diff --git a/code/lib/instrumenter/src/types.ts b/code/lib/instrumenter/src/types.ts
index 4d8097b91cb0..1076d4dd3a1d 100644
--- a/code/lib/instrumenter/src/types.ts
+++ b/code/lib/instrumenter/src/types.ts
@@ -61,7 +61,14 @@ export interface SyncPayload {
 }
 
 export interface State {
-  renderPhase: 'loading' | 'rendering' | 'playing' | 'played' | 'completed' | 'aborted' | 'errored';
+  renderPhase?:
+    | 'loading'
+    | 'rendering'
+    | 'playing'
+    | 'played'
+    | 'completed'
+    | 'aborted'
+    | 'errored';
   isDebugging: boolean;
   isPlaying: boolean;
   isLocked: boolean;
@@ -73,7 +80,7 @@ export interface State {
   ancestors: Call['id'][];
   playUntil?: Call['id'];
   resolvers: Record<Call['id'], Function>;
-  syncTimeout: ReturnType<typeof setTimeout>;
+  syncTimeout?: ReturnType<typeof setTimeout>;
   forwardedException?: Error;
 }
 
diff --git a/code/lib/instrumenter/tsconfig.json b/code/lib/instrumenter/tsconfig.json
index 4c6f20a1be4d..b5a2f9a70918 100644
--- a/code/lib/instrumenter/tsconfig.json
+++ b/code/lib/instrumenter/tsconfig.json
@@ -2,6 +2,6 @@
   "extends": "../../tsconfig.json",
   "include": ["src/**/*"],
   "compilerOptions": {
-    "strict": false
+    "strict": true
   }
 }