diff --git a/src/jsc/bindings/VectorSizeLimit.h b/src/jsc/bindings/VectorSizeLimit.h
new file mode 100644
index 000000000000..cb2b4686f9c5
--- /dev/null
+++ b/src/jsc/bindings/VectorSizeLimit.h
@@ -0,0 +1,20 @@
+#pragma once
+
+#include "root.h"
+#include <wtf/Vector.h>
+
+extern "C" size_t Bun__stringSyntheticAllocationLimit;
+
+namespace Bun {
+
+// The most elements a Vector<T> can hold, lowered by Bun__stringSyntheticAllocationLimit so tests reach it cheaply.
+template<typename T>
+size_t maxVectorSize()
+{
+    constexpr size_t maxBytes = std::numeric_limits<unsigned>::max() >> 1;
+    static_assert(WTF::isValidCapacityForVector<T>(maxBytes / sizeof(T)));
+    static_assert(!WTF::isValidCapacityForVector<T>(maxBytes / sizeof(T) + 1));
+    return std::min(maxBytes, Bun__stringSyntheticAllocationLimit) / sizeof(T);
+}
+
+} // namespace Bun
diff --git a/src/jsc/bindings/webcore/URLPatternTokenizer.cpp b/src/jsc/bindings/webcore/URLPatternTokenizer.cpp
index 4c8d87700c7e..efe491360155 100644
--- a/src/jsc/bindings/webcore/URLPatternTokenizer.cpp
+++ b/src/jsc/bindings/webcore/URLPatternTokenizer.cpp
@@ -28,6 +28,7 @@
 
 #include "ExceptionOr.h"
 #include "URLPatternParser.h"
+#include "VectorSizeLimit.h"
 #include <unicode/utf16.h>
 #include <wtf/text/MakeString.h>
 
@@ -69,8 +70,10 @@ void Tokenizer::seekNextCodePoint(size_t index)
 // https://urlpattern.spec.whatwg.org/#add-a-token
 void Tokenizer::addToken(TokenType currentType, size_t nextPosition, size_t valuePosition, size_t valueLength)
 {
-    m_tokenList.append(Token { currentType, m_index, m_input.substring(valuePosition, valueLength) });
-    m_index = nextPosition;
+    if (m_tokenList.size() >= Bun::maxVectorSize<Token>() || !m_tokenList.tryAppend(Token { currentType, m_index, m_input.substring(valuePosition, valueLength) }))
+        m_tokenAppendFailure = true;
+    else
+        m_index = nextPosition;
 }
 
 // https://urlpattern.spec.whatwg.org/#add-a-token-with-default-length
@@ -109,7 +112,7 @@ ExceptionOr<Vector<Token>> Tokenizer::tokenize()
 {
     ExceptionOr<void> maybeException;
 
-    while (m_index < m_input.length()) {
+    while (m_index < m_input.length() && !m_tokenAppendFailure) {
         if (m_policy == TokenizePolicy::Strict && maybeException.hasException())
             return maybeException.releaseException();
 
@@ -266,6 +269,10 @@ ExceptionOr<Vector<Token>> Tokenizer::tokenize()
     }
 
     addToken(TokenType::End, m_index, m_index);
+
+    if (m_tokenAppendFailure)
+        return Exception { ExceptionCode::TypeError, "URLPattern constructor: Failed to create URLPattern (from input string)"_s };
+
     return WTF::move(m_tokenList);
 }
 
diff --git a/src/jsc/bindings/webcore/URLPatternTokenizer.h b/src/jsc/bindings/webcore/URLPatternTokenizer.h
index fb5a79061687..576b5153883f 100644
--- a/src/jsc/bindings/webcore/URLPatternTokenizer.h
+++ b/src/jsc/bindings/webcore/URLPatternTokenizer.h
@@ -67,6 +67,7 @@ class Tokenizer {
     size_t m_index { 0 };
     size_t m_nextIndex { 0 };
     char32_t m_codepoint;
+    bool m_tokenAppendFailure { false };
 
     void getNextCodePoint();
     void seekNextCodePoint(size_t index);
diff --git a/test/js/web/urlpattern/urlpattern.test.ts b/test/js/web/urlpattern/urlpattern.test.ts
index c2a727ab5b15..2edef8129210 100644
--- a/test/js/web/urlpattern/urlpattern.test.ts
+++ b/test/js/web/urlpattern/urlpattern.test.ts
@@ -1,6 +1,7 @@
 // Test data from Web Platform Tests
 // https://github.com/web-platform-tests/wpt/blob/master/LICENSE.md
-import { describe, expect, test } from "bun:test";
+import { setSyntheticAllocationLimitForTesting } from "bun:internal-for-testing";
+import { afterAll, beforeAll, describe, expect, test } from "bun:test";
 import testData from "./urlpatterntestdata.json";
 
 const kComponents = ["protocol", "username", "password", "hostname", "port", "pathname", "search", "hash"] as const;
@@ -206,4 +207,55 @@ describe("URLPattern", () => {
       expect(new URLPattern({ pathname: "/a/:foo/:baz([a-z]+)?/b/*" }).hasRegExpGroups).toBe(true);
     });
   });
+
+  // The tokenizer keeps one token (40 bytes or more) per code point in a
+  // WTF::Vector, which holds at most 2^31 - 1 bytes. A pattern near 52 million
+  // characters used to abort the process when that Vector could not grow. The
+  // bound follows the synthetic allocation limit, so 1 MiB puts it below 64 Ki.
+  describe("a pattern with more tokens than the token list can hold throws", () => {
+    const dots = (length: number) => Buffer.alloc(length, ".").toString();
+    const message = "URLPattern constructor: Failed to create URLPattern (from input string)";
+    const tooLong = 64 * 1024;
+    const fits = 8 * 1024;
+
+    let originalLimit: number;
+    beforeAll(() => {
+      originalLimit = setSyntheticAllocationLimitForTesting(1024 * 1024);
+    });
+    afterAll(() => {
+      setSyntheticAllocationLimitForTesting(originalLimit);
+    });
+
+    test.each(["username", "password", "hostname", "pathname", "search", "hash"] as const)("in %s", component => {
+      expect(() => new URLPattern({ [component]: dots(tooLong) })).toThrow(message);
+    });
+
+    test("in a constructor string", () => {
+      expect(() => new URLPattern("https://example.com/" + dots(tooLong))).toThrow(message);
+      expect(new URLPattern("https://example.com/" + dots(fits)).test("https://example.com/" + dots(fits))).toBe(true);
+    });
+
+    test("in a pathname inherited from baseURL", () => {
+      expect(() => new URLPattern({ search: "a", baseURL: "https://example.com/" + dots(tooLong) })).toThrow(message);
+    });
+
+    // Find the longest pathname that parses. It must come back whole: the
+    // End token counts against the bound too, and without it the parser
+    // would drop the pending text instead of throwing.
+    test("at the exact bound, and one code point below it parses whole", () => {
+      let low = fits;
+      let high = tooLong;
+      while (low + 1 < high) {
+        const length = (low + high) >>> 1;
+        try {
+          new URLPattern({ pathname: dots(length) });
+          low = length;
+        } catch {
+          high = length;
+        }
+      }
+      expect(new URLPattern({ pathname: dots(low) }).pathname).toBe(dots(low));
+      expect(() => new URLPattern({ pathname: dots(high) })).toThrow(message);
+    });
+  });
 });