diff --git a/packages/connect/src/protocol-connect/end-stream.ts b/packages/connect/src/protocol-connect/end-stream.ts
index 7ad054df6..d6ec07e8d 100644
--- a/packages/connect/src/protocol-connect/end-stream.ts
+++ b/packages/connect/src/protocol-connect/end-stream.ts
@@ -34,7 +34,7 @@ export const endStreamFlag = 0b00000010;
  */
 export interface EndStreamResponse {
   metadata: Headers;
-  error?: ConnectError;
+  error?: ConnectError | undefined;
 }
 
 /**
diff --git a/packages/connect/src/protocol/async-iterable.ts b/packages/connect/src/protocol/async-iterable.ts
index 40e19ea91..4d05056cf 100644
--- a/packages/connect/src/protocol/async-iterable.ts
+++ b/packages/connect/src/protocol/async-iterable.ts
@@ -1069,6 +1069,29 @@ interface Abortable {
 
 type AbortState = "rethrown" | "completed" | "caught";
 
+function assertHasThrow(
+  t: unknown,
+  message: string
+): asserts t is {
+  throw: CallableFunction;
+} {
+  if (
+    typeof t === "object" &&
+    t !== null &&
+    "throw" in t &&
+    typeof t.throw === "function"
+  ) {
+    return;
+  }
+  throw new Error(message);
+}
+
+const hasReturn = (t: unknown): t is { return: CallableFunction } =>
+  typeof t === "object" &&
+  t !== null &&
+  "return" in t &&
+  typeof t.return === "function";
+
 /**
  * Wrap the given iterable and return an iterable with an abort() method.
  *
@@ -1101,11 +1124,8 @@ type AbortState = "rethrown" | "completed" | "caught";
 export function makeIterableAbortable<T>(
   iterable: AsyncIterable<T>
 ): AsyncIterable<T> & Abortable {
-  const innerCandidate = iterable[Symbol.asyncIterator]();
-  if (innerCandidate.throw === undefined) {
-    throw new Error("AsyncIterable does not implement throw");
-  }
-  const inner = innerCandidate as Required<AsyncIterator<T>>;
+  const inner = iterable[Symbol.asyncIterator]();
+  assertHasThrow(inner, "AsyncIterable does not implement throw");
   let aborted: { reason: unknown; state: Promise<AbortState> } | undefined;
   let resultPromise: Promise<IteratorResult<T>> | undefined;
   let it: AsyncIterator<T> = {
@@ -1119,7 +1139,7 @@ export function makeIterableAbortable<T>(
       return inner.throw(e);
     },
   };
-  if (innerCandidate.return === undefined) {
+  if (hasReturn(inner)) {
     it = {
       ...it,
       return(value?: unknown): Promise<IteratorResult<T>> {
diff --git a/packages/connect/src/protocol/compression.ts b/packages/connect/src/protocol/compression.ts
index d4aefd188..9da0595c7 100644
--- a/packages/connect/src/protocol/compression.ts
+++ b/packages/connect/src/protocol/compression.ts
@@ -61,7 +61,7 @@ export function compressionNegotiate(
 ): {
   request: Compression | null;
   response: Compression | null;
-  error?: ConnectError;
+  error?: ConnectError | undefined;
 } {
   let request = null;
   let response = null;
diff --git a/packages/connect/src/protocol/universal-handler.ts b/packages/connect/src/protocol/universal-handler.ts
index c8bbe3c31..aa8bfadad 100644
--- a/packages/connect/src/protocol/universal-handler.ts
+++ b/packages/connect/src/protocol/universal-handler.ts
@@ -77,12 +77,12 @@ export interface UniversalHandlerOptions {
   /**
    * Options for the JSON format.
    */
-  jsonOptions?: Partial<JsonReadOptions & JsonWriteOptions>;
+  jsonOptions?: Partial<JsonReadOptions & JsonWriteOptions> | undefined;
 
   /**
    * Options for the binary wire format.
    */
-  binaryOptions?: Partial<BinaryReadOptions & BinaryWriteOptions>;
+  binaryOptions?: Partial<BinaryReadOptions & BinaryWriteOptions> | undefined;
 
   maxDeadlineDurationMs: number; // TODO TCN-785
   shutdownSignal: AbortSignal; // TODO TCN-919
diff --git a/packages/example/tsconfig.json b/packages/example/tsconfig.json
index f6c1c2f6a..daefc1c50 100644
--- a/packages/example/tsconfig.json
+++ b/packages/example/tsconfig.json
@@ -6,6 +6,7 @@
     "lib": ["ESNext", "DOM"],
     "moduleResolution": "Node",
     "strict": true,
+    "exactOptionalPropertyTypes": true,
     "sourceMap": true,
     "resolveJsonModule": true,
     "isolatedModules": true,
diff --git a/tsconfig.base.json b/tsconfig.base.json
index 405093060..0edc686c8 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -17,6 +17,7 @@
     "strictFunctionTypes": true,
     "strictBindCallApply": true,
     "strictPropertyInitialization": true,
+    "exactOptionalPropertyTypes": true,
     "noImplicitThis": true,
     "useUnknownInCatchVariables": true,
     "noUnusedLocals": true,