diff --git a/src/cjs.ts b/src/cjs.ts
index e78ebde..eb2432b 100644
--- a/src/cjs.ts
+++ b/src/cjs.ts
@@ -35,24 +35,30 @@ export function interopDefault(sourceModule: any): any {
   if (!isObject(sourceModule) || !("default" in sourceModule)) {
     return sourceModule;
   }
-  const newModule = sourceModule.default;
+  const defaultValue = sourceModule.default;
+  if (defaultValue === undefined || defaultValue === null) {
+    return sourceModule;
+  }
+  if (typeof defaultValue !== "object") {
+    return defaultValue;
+  }
   for (const key in sourceModule) {
     if (key === "default") {
       try {
-        if (!(key in newModule)) {
-          Object.defineProperty(newModule, key, {
+        if (!(key in defaultValue)) {
+          Object.defineProperty(defaultValue, key, {
             enumerable: false,
             configurable: false,
             get() {
-              return newModule;
+              return defaultValue;
             },
           });
         }
       } catch {}
     } else {
       try {
-        if (!(key in newModule)) {
-          Object.defineProperty(newModule, key, {
+        if (!(key in defaultValue)) {
+          Object.defineProperty(defaultValue, key, {
             enumerable: true,
             configurable: true,
             get() {
@@ -63,5 +69,5 @@ export function interopDefault(sourceModule: any): any {
       } catch {}
     }
   }
-  return newModule;
+  return defaultValue;
 }
diff --git a/test/interop.test.ts b/test/interop.test.ts
index 2e2f2b9..64f9f0c 100644
--- a/test/interop.test.ts
+++ b/test/interop.test.ts
@@ -16,6 +16,14 @@ const tests = [
     { named: 1, default: { x: 2 } },
     { named: 1, x: 2 },
   ],
+  [
+    { default: null, x: 1 }, // eslint-disable-line unicorn/no-null
+    { default: null, x: 1 }, // eslint-disable-line unicorn/no-null
+  ],
+  [
+    { default: undefined, x: 1 },
+    { default: undefined, x: 1 },
+  ],
 ];
 
 describe("interopDefault", () => {
@@ -24,7 +32,9 @@ describe("interopDefault", () => {
       const interop = interopDefault(input);
       expect(interop).to.deep.equal(result);
       if (typeof input === "object" && "default" in input) {
-        expect(interop.default).to.deep.equal(result);
+        expect(interop.default).to.deep.equal(
+          "default" in (result as any) ? (result as any).default : result,
+        );
       } else {
         expect(interop).to.deep.equal(result);
       }