diff --git a/JSTests/wasm/js-api/exception-getarg-index-enforce-range.js b/JSTests/wasm/js-api/exception-getarg-index-enforce-range.js
new file mode 100644
index 0000000000000..aa635be3e57d8
--- /dev/null
+++ b/JSTests/wasm/js-api/exception-getarg-index-enforce-range.js
@@ -0,0 +1,75 @@
+import * as assert from '../assert.js';
+
+// https://webassembly.github.io/spec/js-api/#exceptions
+//   any getArg(Tag exceptionTag, [EnforceRange] unsigned long index);
+// A WebIDL [EnforceRange] conversion that fails is a TypeError. Only an index that converts and is
+// then >= the payload size is a RangeError.
+
+const tag = new WebAssembly.Tag({ parameters: ["i32", "f64"] });
+const exception = new WebAssembly.Exception(tag, [5, 6.5]);
+
+const notAnUnsignedLong = [
+    -1,
+    -1.5,
+    2 ** 32,
+    2 ** 32 + 0.5,
+    2 ** 53,
+    Number.MAX_VALUE,
+    NaN,
+    Infinity,
+    -Infinity,
+    undefined,
+    "x",
+    "0x100000000",
+    {},
+    { valueOf() { return -1; } },
+    { valueOf() { return 2 ** 32; } },
+];
+for (const index of notAnUnsignedLong)
+    assert.throws(() => exception.getArg(tag, index), TypeError, "Expect an integer argument in the range: [0, 2^32 - 1]");
+
+// These convert to 0 or 1: ToNumber, -0 becomes +0, then the integer part is taken.
+assert.eq(exception.getArg(tag, 0), 5);
+assert.eq(exception.getArg(tag, -0), 5);
+assert.eq(exception.getArg(tag, -0.5), 5);
+assert.eq(exception.getArg(tag, 0.9), 5);
+assert.eq(exception.getArg(tag, null), 5);
+assert.eq(exception.getArg(tag, false), 5);
+assert.eq(exception.getArg(tag, ""), 5);
+assert.eq(exception.getArg(tag, 1), 6.5);
+assert.eq(exception.getArg(tag, 1.99), 6.5);
+assert.eq(exception.getArg(tag, "1"), 6.5);
+assert.eq(exception.getArg(tag, true), 6.5);
+assert.eq(exception.getArg(tag, [1]), 6.5);
+
+let valueOfCalls = 0;
+assert.eq(exception.getArg(tag, { valueOf() { ++valueOfCalls; return 1; } }), 6.5);
+assert.eq(valueOfCalls, 1);
+
+// A valid unsigned long past the payload is still a RangeError.
+for (const index of [2, 2.5, "2", 2 ** 31, 2 ** 32 - 1])
+    assert.throws(() => exception.getArg(tag, index), RangeError, "WebAssembly.Exception.getArg(): Index out of range");
+
+// An empty payload: every index is out of range, but the conversion still comes first.
+{
+    const emptyTag = new WebAssembly.Tag({ parameters: [] });
+    const empty = new WebAssembly.Exception(emptyTag, []);
+    assert.throws(() => empty.getArg(emptyTag, 0), RangeError, "WebAssembly.Exception.getArg(): Index out of range");
+    assert.throws(() => empty.getArg(emptyTag, -1), TypeError, "Expect an integer argument in the range: [0, 2^32 - 1]");
+    assert.throws(() => empty.getArg(emptyTag, undefined), TypeError, "Expect an integer argument in the range: [0, 2^32 - 1]");
+}
+
+// The index is converted before the tag is compared with the exception's tag.
+{
+    const otherTag = new WebAssembly.Tag({ parameters: ["i32", "f64"] });
+    assert.throws(() => exception.getArg(otherTag, -1), TypeError, "Expect an integer argument in the range: [0, 2^32 - 1]");
+    assert.throws(() => exception.getArg(otherTag, 0), TypeError, "WebAssembly.Exception.getArg(): First argument does not match the exception tag");
+}
+
+// ToNumber itself can throw; that exception propagates unchanged.
+assert.throws(() => exception.getArg(tag, Symbol()), TypeError, "");
+assert.throws(() => exception.getArg(tag, 0n), TypeError, "");
+{
+    const error = new Error("from valueOf");
+    assert.throwsExactly(() => exception.getArg(tag, { valueOf() { throw error; } }), error);
+}
diff --git a/JSTests/wasm/v8/exceptions-api.js b/JSTests/wasm/v8/exceptions-api.js
index 91d53681456c6..9a48dbd2e6de5 100644
--- a/JSTests/wasm/v8/exceptions-api.js
+++ b/JSTests/wasm/v8/exceptions-api.js
@@ -200,8 +200,8 @@ function TestGetArgHelper(types_str, types, values) {
       /First argument must be a WebAssembly.Tag/);
   assertThrows(() => exception.getArg({}, 0), TypeError,
       /First argument must be a WebAssembly.Tag/);
-  //assertThrows(() => exception.getArg(tag, undefined), TypeError,
-      ///Index must be convertible to a valid number/);
+  assertThrows(() => exception.getArg(tag, undefined), TypeError,
+      /Expect an integer argument in the range: \[0, 2\^32 - 1\]/);
   assertThrows(() => exception.getArg(tag, 0xFFFFFFFF), RangeError,
       /Index out of range/);
   let wrong_tag = new WebAssembly.Tag({parameters: ['i32']});
diff --git a/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any-expected.txt
index 383f6cad7eee1..723d5821bffa0 100644
--- a/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any-expected.txt
+++ b/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any-expected.txt
@@ -2,6 +2,8 @@
 PASS Missing arguments
 PASS Invalid exception argument
 PASS Index out of bounds
-PASS Getting out-of-range argument
+FAIL Getting out-of-range argument assert_throws_js: function "() => exn.getArg(tag, value)" threw object "TypeError: Expect an integer argument in the range: [0, 2^32 - 1]" ("TypeError") expected instance of function "function RangeError() {
+    [native code]
+}" ("RangeError")
 PASS getArg
 
diff --git a/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any.worker-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any.worker-expected.txt
index 383f6cad7eee1..723d5821bffa0 100644
--- a/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any.worker-expected.txt
+++ b/LayoutTests/imported/w3c/web-platform-tests/wasm/jsapi/exception/getArg.tentative.any.worker-expected.txt
@@ -2,6 +2,8 @@
 PASS Missing arguments
 PASS Invalid exception argument
 PASS Index out of bounds
-PASS Getting out-of-range argument
+FAIL Getting out-of-range argument assert_throws_js: function "() => exn.getArg(tag, value)" threw object "TypeError: Expect an integer argument in the range: [0, 2^32 - 1]" ("TypeError") expected instance of function "function RangeError() {
+    [native code]
+}" ("RangeError")
 PASS getArg
 
diff --git a/Source/JavaScriptCore/wasm/js/WebAssemblyExceptionPrototype.cpp b/Source/JavaScriptCore/wasm/js/WebAssemblyExceptionPrototype.cpp
index 8c1fe0f3b42be..5405b9708992a 100644
--- a/Source/JavaScriptCore/wasm/js/WebAssemblyExceptionPrototype.cpp
+++ b/Source/JavaScriptCore/wasm/js/WebAssemblyExceptionPrototype.cpp
@@ -115,7 +115,7 @@ JSC_DEFINE_HOST_FUNCTION(webAssemblyExceptionProtoFuncGetArg, (JSGlobalObject* g
     if (!tag) [[unlikely]]
         return throwVMTypeError(globalObject, throwScope, formatMessage("First argument must be a WebAssembly.Tag"_s));
 
-    uint32_t index = toNonWrappingUint32(globalObject, callFrame->argument(1), ErrorType::RangeError);
+    uint32_t index = toNonWrappingUint32(globalObject, callFrame->argument(1));
     RETURN_IF_EXCEPTION(throwScope, { });
 
     if (jsException->tag() != tag->tag()) [[unlikely]]