diff --git a/packages/actor-memory-expression/src/memory_calculator.ts b/packages/actor-memory-expression/src/memory_calculator.ts
index 842545671..4e4beb728 100644
--- a/packages/actor-memory-expression/src/memory_calculator.ts
+++ b/packages/actor-memory-expression/src/memory_calculator.ts
@@ -104,6 +104,7 @@ math.import(
  *
  * This is custom function designed to be injected into the math expression evaluator,
  * allowing expressions like `get(input, 'user.settings.memory', 512)` or `get(input, 'startUrls.length', 10)` to get array length.
+ * Only own properties are followed, so inherited members like `toString` resolve to `defaultVal`.
  *
  * @param obj The source object to search within.
  * @param path A dot-separated string representing the nested path (e.g., "input.payload.size").
@@ -111,7 +112,14 @@ math.import(
  * @returns The retrieved value, or `defaultVal` if the path is unreachable.
  */
 const customGetFunc = (obj: any, path: string, defaultVal?: number) => {
-    return path.split('.').reduce((current, key) => current?.[key], obj) ?? defaultVal;
+    return (
+        path
+            .split('.')
+            .reduce(
+                (current, key) => (current != null && Object.hasOwn(current, key) ? current[key] : undefined),
+                obj,
+            ) ?? defaultVal
+    );
 };
 
 /**
diff --git a/test/memory_calculator.test.ts b/test/memory_calculator.test.ts
index 2dc77b887..f7476e18f 100644
--- a/test/memory_calculator.test.ts
+++ b/test/memory_calculator.test.ts
@@ -55,6 +55,25 @@ describe('calculateDefaultMemoryFromExpression', () => {
             expect(result).toBe(512);
         });
 
+        it('should resolve array and string length with get()', async () => {
+            const context = { input: { startUrls: ['a', 'b', 'c', 'd'], name: 'abcdefgh' }, runOptions: {} };
+            expect(await calculateRunDynamicMemory("get(input, 'startUrls.length', 1) * 256", context)).toBe(1024);
+            expect(await calculateRunDynamicMemory("get(input, 'name.length', 1) * 256", context)).toBe(2048);
+        });
+
+        it.each([
+            'constructor',
+            'constructor.constructor',
+            '__proto__',
+            'toString',
+            'nested.hasOwnProperty',
+            'count.toFixed',
+        ])('should use get() default value for inherited property %s', async (path) => {
+            const context = { input: { nested: {}, count: 5 }, runOptions: {} };
+            const result = await calculateRunDynamicMemory(`get(input, '${path}', 512)`, context);
+            expect(result).toBe(512);
+        });
+
         describe('matching string enum values with compareText()', () => {
             const expr = "compareText(input.dataOutput, 'full detail') == 0 ? 4096 : 1024";