diff --git a/lib/binary_parser.ts b/lib/binary_parser.ts
index cf511f6..0335f71 100644
--- a/lib/binary_parser.ts
+++ b/lib/binary_parser.ts
@@ -1353,7 +1353,10 @@ export class Parser {
     }
 
     if (isHash) {
-      ctx.pushCode(`${lhs}[${item}.${key}] = ${item};`);
+      // defineProperty so that keys like "__proto__" become own properties
+      ctx.pushCode(
+        `Object.defineProperty(${lhs}, ${item}.${key}, { value: ${item}, enumerable: true, writable: true, configurable: true });`,
+      );
     } else {
       ctx.pushCode(`${lhs}.push(${item});`);
     }
diff --git a/test/composite_parser.ts b/test/composite_parser.ts
index b369b54..319b6ff 100644
--- a/test/composite_parser.ts
+++ b/test/composite_parser.ts
@@ -287,6 +287,31 @@ function compositeParserTests(
           },
         });
       });
+      it("should store __proto__ key as an own property of associative arrays", () => {
+        const parser = Parser.start().array("a", {
+          type: Parser.start()
+            .uint8("l")
+            .string("k", { length: "l" })
+            .uint8("evil"),
+          lengthInBytes: 11,
+          key: "k",
+        });
+        const buffer = factory([
+          9,
+          ...Array.from("__proto__", (c) => c.charCodeAt(0)),
+          1,
+        ]);
+        const result = parser.parse(buffer);
+
+        expect(Object.keys(result.a)).toStrictEqual(["__proto__"]);
+        expect(Object.getPrototypeOf(result.a)).toBe(Object.prototype);
+        expect(result.a.evil).toBeUndefined();
+        expect(result.a["__proto__"]).toStrictEqual({
+          l: 9,
+          k: "__proto__",
+          evil: 1,
+        });
+      });
       it("should use formatter to transform parsed array", () => {
         const parser = Parser.start().array("data", {
           type: "uint8",