diff --git a/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp b/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp
index 5788de6c2b..0aeabb68a7 100644
--- a/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp
@@ -201,7 +201,7 @@ size_t array_buffer_byte_length(ArrayBuffer const& array_buffer, ArrayBuffer::Or
 ThrowCompletionOr<void> detach_array_buffer(VM& vm, ArrayBuffer& array_buffer, Optional<Value> key)
 {
     // 1. Assert: IsSharedArrayBuffer(arrayBuffer) is false.
-    // FIXME: Check for shared buffer
+    VERIFY(!array_buffer.is_shared_array_buffer());
 
     // 2. If key is not present, set key to undefined.
     if (!key.has_value())
diff --git a/Userland/Libraries/LibJS/Runtime/ArrayBufferPrototype.cpp b/Userland/Libraries/LibJS/Runtime/ArrayBufferPrototype.cpp
index 0039aa1a61..7b63f3599d 100644
--- a/Userland/Libraries/LibJS/Runtime/ArrayBufferPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ArrayBufferPrototype.cpp
@@ -174,7 +174,8 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayBufferPrototype::slice)
     auto array_buffer_object = TRY(typed_this_value(vm));
 
     // 3. If IsSharedArrayBuffer(O) is true, throw a TypeError exception.
-    // FIXME: Check for shared buffer
+    if (array_buffer_object->is_shared_array_buffer())
+        return vm.throw_completion<TypeError>(ErrorType::SharedArrayBuffer);
 
     // 4. If IsDetachedBuffer(O) is true, throw a TypeError exception.
     if (array_buffer_object->is_detached())
@@ -226,7 +227,8 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayBufferPrototype::slice)
     auto* new_array_buffer_object = static_cast<ArrayBuffer*>(new_array_buffer.ptr());
 
     // 18. If IsSharedArrayBuffer(new) is true, throw a TypeError exception.
-    // FIXME: Check for shared buffer
+    if (new_array_buffer_object->is_shared_array_buffer())
+        return vm.throw_completion<TypeError>(ErrorType::SharedArrayBuffer);
 
     // 19. If IsDetachedBuffer(new) is true, throw a TypeError exception.
     if (new_array_buffer_object->is_detached())
diff --git a/Userland/Libraries/LibJS/Runtime/SharedArrayBufferPrototype.cpp b/Userland/Libraries/LibJS/Runtime/SharedArrayBufferPrototype.cpp
index 5df8ef92d8..dbf7aa2992 100644
--- a/Userland/Libraries/LibJS/Runtime/SharedArrayBufferPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/SharedArrayBufferPrototype.cpp
@@ -40,7 +40,8 @@ JS_DEFINE_NATIVE_FUNCTION(SharedArrayBufferPrototype::byte_length_getter)
     auto array_buffer_object = TRY(typed_this_value(vm));
 
     // 3. If IsSharedArrayBuffer(O) is false, throw a TypeError exception.
-    // FIXME: Check for shared buffer
+    if (!array_buffer_object->is_shared_array_buffer())
+        return vm.throw_completion<TypeError>(ErrorType::NotASharedArrayBuffer);
 
     // 4. Let length be O.[[ArrayBufferByteLength]].
     // 5. Return 𝔽(length).
@@ -60,7 +61,8 @@ JS_DEFINE_NATIVE_FUNCTION(SharedArrayBufferPrototype::slice)
     auto array_buffer_object = TRY(typed_this_value(vm));
 
     // 3. If IsSharedArrayBuffer(O) is false, throw a TypeError exception.
-    // FIXME: Check for shared buffer
+    if (!array_buffer_object->is_shared_array_buffer())
+        return vm.throw_completion<TypeError>(ErrorType::NotASharedArrayBuffer);
 
     // 4. Let len be O.[[ArrayBufferByteLength]].
     auto length = array_buffer_object->byte_length();
@@ -108,7 +110,8 @@ JS_DEFINE_NATIVE_FUNCTION(SharedArrayBufferPrototype::slice)
     auto* new_array_buffer_object = static_cast<ArrayBuffer*>(new_array_buffer.ptr());
 
     // 17. If IsSharedArrayBuffer(new) is true, throw a TypeError exception.
-    // FIXME: Check for shared buffer
+    if (!new_array_buffer_object->is_shared_array_buffer())
+        return vm.throw_completion<TypeError>(ErrorType::NotASharedArrayBuffer);
 
     // 18. If new.[[ArrayBufferData]] is O.[[ArrayBufferData]], throw a TypeError exception.
     if (new_array_buffer == array_buffer_object)
diff --git a/Userland/Libraries/LibJS/Tests/builtins/ArrayBuffer/ArrayBuffer.prototype.slice.js b/Userland/Libraries/LibJS/Tests/builtins/ArrayBuffer/ArrayBuffer.prototype.slice.js
index a8dd527d9b..311a774725 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/ArrayBuffer/ArrayBuffer.prototype.slice.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/ArrayBuffer/ArrayBuffer.prototype.slice.js
@@ -1,3 +1,11 @@
+describe("errors", () => {
+    test("called on SharedArrayBuffer object", () => {
+        expect(() => {
+            ArrayBuffer.prototype.slice.call(new SharedArrayBuffer());
+        }).toThrowWithMessage(TypeError, "The array buffer object cannot be a SharedArrayBuffer");
+    });
+});
+
 test("single parameter", () => {
     const buffer = new ArrayBuffer(16);
     const fullView = new Int32Array(buffer);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.byteLength.js b/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.byteLength.js
index a832d9425b..87d1be7f88 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.byteLength.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.byteLength.js
@@ -1,3 +1,18 @@
+describe("errors", () => {
+    test("called on non-SharedArrayBuffer object", () => {
+        expect(() => {
+            SharedArrayBuffer.prototype.byteLength;
+        }).toThrowWithMessage(TypeError, "Not an object of type SharedArrayBuffer");
+
+        let byteLength = Object.getOwnPropertyDescriptor(SharedArrayBuffer.prototype, "byteLength");
+        let getter = byteLength.get;
+
+        expect(() => {
+            getter.call(new ArrayBuffer());
+        }).toThrowWithMessage(TypeError, "The array buffer object must be a SharedArrayBuffer");
+    });
+});
+
 test("basic functionality", () => {
     expect(new SharedArrayBuffer().byteLength).toBe(0);
     expect(new SharedArrayBuffer(1).byteLength).toBe(1);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.slice.js b/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.slice.js
index a46cdaf9ef..0e492d51d3 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.slice.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/SharedArrayBuffer/SharedArrayBuffer.prototype.slice.js
@@ -1,3 +1,15 @@
+describe("errors", () => {
+    test("called on non-SharedArrayBuffer object", () => {
+        expect(() => {
+            SharedArrayBuffer.prototype.slice(Symbol.hasInstance);
+        }).toThrowWithMessage(TypeError, "Not an object of type SharedArrayBuffer");
+
+        expect(() => {
+            SharedArrayBuffer.prototype.slice.call(new ArrayBuffer());
+        }).toThrowWithMessage(TypeError, "The array buffer object must be a SharedArrayBuffer");
+    });
+});
+
 test("single parameter", () => {
     const buffer = new SharedArrayBuffer(16);
     const fullView = new Int32Array(buffer);