diff --git a/lib/src/array/forEach.ts b/lib/src/array/forEach.ts
index 95060a2d..c3a74b96 100644
--- a/lib/src/array/forEach.ts
+++ b/lib/src/array/forEach.ts
@@ -6,6 +6,7 @@
  * Licensed under the MIT license.
  */
 
+import { isStrictNullOrUndefined } from "../helpers/base";
 import { CALL, LENGTH } from "../internal/constants";
 
 /**
@@ -50,12 +51,14 @@ import { CALL, LENGTH } from "../internal/constants";
  * const items = { length: 3, 0: 'item1', 1: 'item2', 2: 'item3' };
  * ```
  */
-export function arrForEach<T = any>(theArray: ArrayLike<T>, callbackfn: (value: T, index: number, array: T[]) => void | number, thisArg?: any): void {
+export function arrForEach<T = any>(theArray: ArrayLike<T>, callbackfn: (value: T, index: number, array: T[]) => void | number, thisArg?: any): void;
+export function arrForEach<T = any>(theArray: ArrayLike<T>, callbackfn: (value: T, index: number, array: ArrayLike<T>) => void | number, thisArg?: any): void;
+export function arrForEach<T = any, A extends ArrayLike<T> = ArrayLike<T>>(theArray: A, callbackfn: (value: T, index: number, array: A) => void | number, thisArg?: any): void {
     if (theArray) {
         const len = theArray[LENGTH] >>> 0;
         for (let idx = 0; idx < len; idx++) {
             if (idx in theArray) {
-                if (callbackfn[CALL](thisArg || theArray, theArray[idx], idx, theArray) === -1) {
+                if (callbackfn[CALL](isStrictNullOrUndefined(thisArg) ? theArray as any : thisArg, theArray[idx], idx, theArray) === -1) {
                     break;
                 }
             }
diff --git a/lib/src/iterator/forOf.ts b/lib/src/iterator/forOf.ts
index 45e62ca1..eeb34954 100644
--- a/lib/src/iterator/forOf.ts
+++ b/lib/src/iterator/forOf.ts
@@ -7,6 +7,7 @@
  */
 
 import { ICachedValue, createCachedValue } from "../helpers/cache";
+import { isStrictNullOrUndefined } from "../helpers/base";
 import { CALL, NULL_VALUE, UNDEF_VALUE } from "../internal/constants";
 import { getKnownSymbol } from "../symbol/symbol";
 import { WellKnownSymbols } from "../symbol/well_known";
@@ -68,7 +69,7 @@ export function iterForOf<T>(iter: Iterator<T> | Iterable<T>, callbackfn: (value
             try {
                 let count = 0;
                 while(!(iterResult = iter.next()).done) {
-                    if (callbackfn[CALL](thisArg || iter, iterResult.value, count, iter) === -1) {
+                    if (callbackfn[CALL](isStrictNullOrUndefined(thisArg) ? iter : thisArg, iterResult.value, count, iter) === -1) {
                         break;
                     }
         
diff --git a/lib/src/object/for_each_key.ts b/lib/src/object/for_each_key.ts
index 5fa17e78..19e86281 100644
--- a/lib/src/object/for_each_key.ts
+++ b/lib/src/object/for_each_key.ts
@@ -6,7 +6,7 @@
  * Licensed under the MIT license.
  */
 
-import { isFunction, isObject } from "../helpers/base";
+import { isFunction, isObject, isStrictNullOrUndefined } from "../helpers/base";
 import { CALL } from "../internal/constants";
 import { objHasOwn } from "./has_own";
 
@@ -42,7 +42,7 @@ export function objForEachKey<T>(theObject: T, callbackfn: (key: string, value:
     if (theObject && (isObject(theObject) || isFunction(theObject))) {
         for (const prop in theObject) {
             if (objHasOwn(theObject, prop)) {
-                if (callbackfn[CALL](thisArg || theObject, prop, theObject[prop as keyof T]) === -1) {
+                if (callbackfn[CALL](isStrictNullOrUndefined(thisArg) ? theObject : thisArg, prop, theObject[prop as keyof T]) === -1) {
                     break;
                 }
             }
diff --git a/lib/test/src/common/helpers/array.test.ts b/lib/test/src/common/helpers/array.test.ts
index 85a8ecd4..1aa33d23 100644
--- a/lib/test/src/common/helpers/array.test.ts
+++ b/lib/test/src/common/helpers/array.test.ts
@@ -152,6 +152,46 @@ describe("array helpers", () => {
             }
 
         });
+
+        it("Validate falsy thisArg values are used correctly (not replaced by array)", () => {
+            const arr = [1, 2, 3];
+            let capturedThis: any;
+
+
+            // omitted thisArg → falls back to the array
+            arrForEach(arr, function(this: any) {
+                capturedThis = this;
+            });
+            assert.strictEqual(capturedThis, arr, "omitting thisArg should use the array as this");
+
+            // explicit undefined → same as omitted
+            arrForEach(arr, function(this: any) {
+                capturedThis = this;
+            }, undefined);
+            assert.strictEqual(capturedThis, arr, "explicit undefined thisArg should use the array as this");
+
+            // null → same as undefined, falls back to array
+            arrForEach(arr, function(this: any) {
+                capturedThis = this;
+            }, null);
+            assert.strictEqual(capturedThis, arr, "null thisArg should use the array as this");
+
+            // falsy-but-not-null/undefined values are used as-is
+            arrForEach(arr, function(this: any) {
+                capturedThis = this;
+            }, 0);
+            assert.strictEqual(capturedThis, 0, "thisArg of 0 should be used as-is");
+
+            arrForEach(arr, function(this: any) {
+                capturedThis = this;
+            }, "");
+            assert.strictEqual(capturedThis, "", "thisArg of empty string should be used as-is");
+
+            arrForEach(arr, function(this: any) {
+                capturedThis = this;
+            }, false);
+            assert.strictEqual(capturedThis, false, "thisArg of false should be used as-is");
+        });
     });
 
     describe("arrAppend", () => {
diff --git a/lib/test/src/common/iterator/forOf.test.ts b/lib/test/src/common/iterator/forOf.test.ts
index b23cb5f4..401cf66f 100644
--- a/lib/test/src/common/iterator/forOf.test.ts
+++ b/lib/test/src/common/iterator/forOf.test.ts
@@ -176,5 +176,49 @@ describe("create iterator helpers", () => {
             assert.equal(values[0], 10);
             assert.equal(values[1], 20);
         });
+
+        it("omitting or passing null/undefined thisArg falls back to the iterator", () => {
+            let capturedThis: any;
+
+            // omitted thisArg → falls back to the iterator
+            const iter1 = createArrayIterator([1]);
+            iterForOf(iter1, function(this: any) {
+                capturedThis = this;
+            });
+            assert.strictEqual(capturedThis, iter1, "omitting thisArg should use the iterator as this");
+
+            // explicit undefined → same as omitted
+            const iter2 = createArrayIterator([1]);
+            iterForOf(iter2, function(this: any) {
+                capturedThis = this;
+            }, undefined);
+            assert.strictEqual(capturedThis, iter2, "explicit undefined thisArg should use the iterator as this");
+
+            // null → same as undefined, falls back to iterator
+            const iter3 = createArrayIterator([1]);
+            iterForOf(iter3, function(this: any) {
+                capturedThis = this;
+            }, null);
+            assert.strictEqual(capturedThis, iter3, "null thisArg should use the iterator as this");
+        });
+
+        it("falsy-but-not-null/undefined thisArg values are used as-is", () => {
+            let capturedThis: any;
+
+            iterForOf(createArrayIterator([1]), function(this: any) {
+                capturedThis = this;
+            }, 0);
+            assert.strictEqual(capturedThis, 0, "thisArg of 0 should be used as-is");
+
+            iterForOf(createArrayIterator([1]), function(this: any) {
+                capturedThis = this;
+            }, "");
+            assert.strictEqual(capturedThis, "", "thisArg of empty string should be used as-is");
+
+            iterForOf(createArrayIterator([1]), function(this: any) {
+                capturedThis = this;
+            }, false);
+            assert.strictEqual(capturedThis, false, "thisArg of false should be used as-is");
+        });
     });
 });
\ No newline at end of file
diff --git a/lib/test/src/common/object/for_each_key.test.ts b/lib/test/src/common/object/for_each_key.test.ts
index 6e3789eb..f4c90bcf 100644
--- a/lib/test/src/common/object/for_each_key.test.ts
+++ b/lib/test/src/common/object/for_each_key.test.ts
@@ -37,15 +37,47 @@ describe("object for_each_key tests", () => {
             assert.strictEqual(actualThis, thisObj, "Should use the provided thisArg");
         });
 
-        it("should use the object as thisArg when not provided", () => {
-            const obj = { a: 1, b: 2 };
-            let actualThis: any;
+        it("should use the object as this when thisArg is omitted, undefined, or null", () => {
+            const obj = { a: 1 };
+            let capturedThis: any;
 
+            // omitted thisArg → falls back to the object
             objForEachKey(obj, function(this: any) {
-                actualThis = this;
+                capturedThis = this;
             });
+            assert.strictEqual(capturedThis, obj, "omitting thisArg should use the object as this");
+
+            // explicit undefined → same as omitted
+            objForEachKey(obj, function(this: any) {
+                capturedThis = this;
+            }, undefined);
+            assert.strictEqual(capturedThis, obj, "explicit undefined thisArg should use the object as this");
+
+            // null → same as undefined, falls back to object
+            objForEachKey(obj, function(this: any) {
+                capturedThis = this;
+            }, null);
+            assert.strictEqual(capturedThis, obj, "null thisArg should use the object as this");
+        });
+
+        it("should use falsy-but-not-null/undefined thisArg values as-is", () => {
+            const obj = { a: 1 };
+            let capturedThis: any;
+
+            objForEachKey(obj, function(this: any) {
+                capturedThis = this;
+            }, 0);
+            assert.strictEqual(capturedThis, 0, "thisArg of 0 should be used as-is");
 
-            assert.strictEqual(actualThis, obj, "Should use the object as thisArg when not provided");
+            objForEachKey(obj, function(this: any) {
+                capturedThis = this;
+            }, "");
+            assert.strictEqual(capturedThis, "", "thisArg of empty string should be used as-is");
+
+            objForEachKey(obj, function(this: any) {
+                capturedThis = this;
+            }, false);
+            assert.strictEqual(capturedThis, false, "thisArg of false should be used as-is");
         });
 
         it("should break iteration when callback returns -1", () => {