diff --git a/test/built-ins/Iterator/prototype/flatMap/flattens-iteratable.js b/test/built-ins/Iterator/prototype/flatMap/flattens-iteratable.js
new file mode 100644
index 00000000000..41ad4268dcf
--- /dev/null
+++ b/test/built-ins/Iterator/prototype/flatMap/flattens-iteratable.js
@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.flatMap
+description: >
+  Iterator.prototype.flatMap flattens iterables returned by the mapper
+info: |
+  %Iterator.prototype%.flatMap ( mapper )
+
+includes: [iterators.js, compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+  yield 3;
+}
+
+let iter = g().flatMap((v, count) => {
+  let result = [];
+  for (let i = 0; i < v; ++i) {
+    result.push(v);
+  }
+  return result;
+});
+
+assert.compareArray(Array.from(iter), [1, 2, 2, 3, 3, 3]);
diff --git a/test/built-ins/Iterator/prototype/flatMap/flattens-iterator.js b/test/built-ins/Iterator/prototype/flatMap/flattens-iterator.js
new file mode 100644
index 00000000000..1ef2029d98f
--- /dev/null
+++ b/test/built-ins/Iterator/prototype/flatMap/flattens-iterator.js
@@ -0,0 +1,42 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.flatMap
+description: >
+  Iterator.prototype.flatMap flattens non-iterable iterators returned by the mapper
+info: |
+  %Iterator.prototype%.flatMap ( mapper )
+
+includes: [iterators.js, compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+  yield 3;
+}
+
+let iter = g().flatMap((v, count) => {
+  let i = 0;
+  return {
+    next: function() {
+      if (i < v) {
+        ++i;
+        return {
+          value: v,
+          done: false
+        };
+      } else {
+        return {
+          value: undefined,
+          done: true
+        };
+      }
+    }
+  };
+});
+
+assert.compareArray(Array.from(iter), [1, 2, 2, 3, 3, 3]);
diff --git a/test/built-ins/Iterator/prototype/flatMap/flattens-only-depth-1.js b/test/built-ins/Iterator/prototype/flatMap/flattens-only-depth-1.js
new file mode 100644
index 00000000000..16ecfd93e50
--- /dev/null
+++ b/test/built-ins/Iterator/prototype/flatMap/flattens-only-depth-1.js
@@ -0,0 +1,34 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.flatMap
+description: >
+  Iterator.prototype.flatMap does not flatten recursively
+info: |
+  %Iterator.prototype%.flatMap ( mapper )
+
+includes: [iterators.js, compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+let arr = [
+  {
+    [Symbol.iterator]: function() {
+      throw new Test262Error;
+    }
+  },
+  {
+    next: function() {
+      throw new Test262Error;
+    }
+  }
+];
+
+function* g() {
+  yield arr;
+}
+
+let iter = g().flatMap(v => v);
+
+assert.compareArray(Array.from(iter), arr);
diff --git a/test/built-ins/Iterator/prototype/flatMap/iterable-primitives-are-not-flattened.js b/test/built-ins/Iterator/prototype/flatMap/iterable-primitives-are-not-flattened.js
new file mode 100644
index 00000000000..a04916dc6db
--- /dev/null
+++ b/test/built-ins/Iterator/prototype/flatMap/iterable-primitives-are-not-flattened.js
@@ -0,0 +1,35 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.flatMap
+description: >
+  Iterator.prototype.flatMap does not respect the iterability of any primitive
+info: |
+  %Iterator.prototype%.flatMap ( mapper )
+
+includes: [iterators.js, compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+}
+
+Number.prototype[Symbol.iterator] = function* () {
+  let i = 0;
+  let target = this >>> 0;
+  while (i < target) {
+    yield i;
+    ++i;
+  }
+};
+
+assert.compareArray(Array.from(5), [0, 1, 2, 3, 4]);
+
+assert.throws(TypeError, function () {
+  for(let unused of g().flatMap(v => 5));
+});
+
+let iter = g().flatMap(v => new Number(5));
+assert.compareArray(Array.from(iter), [0, 1, 2, 3, 4]);
diff --git a/test/built-ins/Iterator/prototype/flatMap/iterable-to-iterator-fallback.js b/test/built-ins/Iterator/prototype/flatMap/iterable-to-iterator-fallback.js
new file mode 100644
index 00000000000..12d9803efc8
--- /dev/null
+++ b/test/built-ins/Iterator/prototype/flatMap/iterable-to-iterator-fallback.js
@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.flatMap
+description: >
+  Iterator.prototype.flatMap falls back to treating mapper return values as iterators if the Symbol.iterator property is not callable
+info: |
+  %Iterator.prototype%.flatMap ( mapper )
+
+includes: [iterators.js, compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+}
+
+function* h() {
+  yield 0;
+  yield 1;
+  yield 2;
+}
+
+let iter = g().flatMap(v => {
+  let n = h();
+  return {
+    [Symbol.iterator]: 0,
+    next: () => n.next()
+  };
+});
+
+assert.compareArray(Array.from(iter), [0, 1, 2]);
diff --git a/test/built-ins/Iterator/prototype/flatMap/mapper-args.js b/test/built-ins/Iterator/prototype/flatMap/mapper-args.js
index b7c24c396b0..d8f30ee528e 100644
--- a/test/built-ins/Iterator/prototype/flatMap/mapper-args.js
+++ b/test/built-ins/Iterator/prototype/flatMap/mapper-args.js
@@ -15,6 +15,8 @@ function* g() {
   yield 'a';
   yield 'b';
   yield 'c';
+  yield 'd';
+  yield 'e';
 }
 
 let assertionCount = 0;
@@ -22,22 +24,31 @@ let iter = g().flatMap((v, count) => {
   switch (v) {
     case 'a':
       assert.sameValue(count, 0);
-      break;
+      ++assertionCount;
+      return [0];
     case 'b':
       assert.sameValue(count, 1);
-      break;
+      ++assertionCount;
+      return [0];
     case 'c':
       assert.sameValue(count, 2);
-      break;
+      ++assertionCount;
+      return [1, 2];
+    case 'd':
+      assert.sameValue(count, 3);
+      ++assertionCount;
+      return [3, 4, 5];
+    case 'e':
+      assert.sameValue(count, 4);
+      ++assertionCount;
+      return [6, 7, 8, 9];
     default:
       throw new Error;
   }
-  ++assertionCount;
-  return [v];
 });
 
 assert.sameValue(assertionCount, 0);
 
 for (let i of iter);
 
-assert.sameValue(assertionCount, 3);
+assert.sameValue(assertionCount, 5);
diff --git a/test/built-ins/Iterator/prototype/flatMap/strings-are-not-flattened.js b/test/built-ins/Iterator/prototype/flatMap/strings-are-not-flattened.js
new file mode 100644
index 00000000000..0ee5c93243c
--- /dev/null
+++ b/test/built-ins/Iterator/prototype/flatMap/strings-are-not-flattened.js
@@ -0,0 +1,24 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.flatMap
+description: >
+  Iterator.prototype.flatMap does not respect the iterability of primitive strings
+info: |
+  %Iterator.prototype%.flatMap ( mapper )
+
+includes: [iterators.js, compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+}
+
+assert.throws(TypeError, function () {
+  for(let unused of g().flatMap(v => 'string'));
+});
+
+let iter = g().flatMap(v => new String('string'));
+assert.compareArray(Array.from(iter), ['s', 't', 'r', 'i', 'n', 'g']);