2 files changed, 23 insertions, 3 deletions
diff --git a/src/bun.js/bindings/JSBuffer.cpp b/src/bun.js/bindings/JSBuffer.cpp
index 524007f86..543ef2ea3 100644
--- a/src/bun.js/bindings/JSBuffer.cpp
+++ b/src/bun.js/bindings/JSBuffer.cpp
@@ -742,10 +742,16 @@ static inline JSC::EncodedJSValue jsBufferConstructorFunction_concatBody(JSC::JS
         byteLength += typedArray->length();
     }
 
-    if (callFrame->argumentCount() > 1) {
-        auto byteLengthValue = callFrame->uncheckedArgument(1);
-        byteLength = std::min(byteLength, byteLengthValue.toTypedArrayIndex(lexicalGlobalObject, "totalLength must be a valid number"_s));
+    JSValue totalLengthValue = callFrame->argument(1);
+    if (!totalLengthValue.isUndefined()) {
+        if (UNLIKELY(!totalLengthValue.isNumber())) {
+            throwTypeError(lexicalGlobalObject, throwScope, "totalLength must be a valid number"_s);
+            return JSValue::encode(jsUndefined());
+        }
+
+        auto totalLength = totalLengthValue.toTypedArrayIndex(lexicalGlobalObject, "totalLength must be a valid number"_s);
         RETURN_IF_EXCEPTION(throwScope, {});
+        byteLength = totalLength;
     }
 
     if (byteLength == 0) {
diff --git a/test/js/node/buffer.test.js b/test/js/node/buffer.test.js
index 0256934ce..450129b0e 100644
--- a/test/js/node/buffer.test.js
+++ b/test/js/node/buffer.test.js
@@ -1327,6 +1327,20 @@ it("Buffer.concat", () => {
   expect(Buffer.concat([array1, array2, array3], 222).length).toBe(222);
   expect(Buffer.concat([array1, array2, array3], 222).subarray(0, 128).join("")).toBe("100".repeat(128));
   expect(Buffer.concat([array1, array2, array3], 222).subarray(129, 222).join("")).toBe("200".repeat(222 - 129));
+  expect(() => {
+    Buffer.concat([array1], -1);
+  }).toThrow(RangeError);
+  expect(() => {
+    Buffer.concat([array1], "1");
+  }).toThrow(TypeError);
+  // issue#6570
+  expect(Buffer.concat([array1, array2, array3], undefined).join("")).toBe(
+    array1.join("") + array2.join("") + array3.join(""),
+  );
+  // issue#3639
+  expect(Buffer.concat([array1, array2, array3], 128 * 4).join("")).toBe(
+    array1.join("") + array2.join("") + array3.join("") + Buffer.alloc(128).join(""),
+  );
 });
 
 it("read", () => {