diff --git a/.changeset/preserve-query-param-encoding.md b/.changeset/preserve-query-param-encoding.md
new file mode 100644
index 000000000..57a0dae1c
--- /dev/null
+++ b/.changeset/preserve-query-param-encoding.md
@@ -0,0 +1,9 @@
+---
+"@opennextjs/aws": patch
+---
+
+Preserve percent-encoding of query parameters in `getQueryFromSearchParams`
+
+`getQueryFromSearchParams` iterated over `URLSearchParams.entries()`, which decodes the values. Since `convertToQueryString` does not re-encode them (by design, see #817), any query value containing reserved characters (`&`, `=`, `+`, spaces, ...) was corrupted when the query string was rebuilt for `req.url`. The parser now keeps the values encoded so they round-trip correctly through `convertToQueryString`.
+
+Fixes opennextjs/opennextjs-cloudflare#1134.
diff --git a/packages/open-next/src/overrides/converters/utils.ts b/packages/open-next/src/overrides/converters/utils.ts
index 252b10975..5a1712d68 100644
--- a/packages/open-next/src/overrides/converters/utils.ts
+++ b/packages/open-next/src/overrides/converters/utils.ts
@@ -27,9 +27,23 @@ export function extractHostFromHeaders(
 /**
  * Get the query object from an URLSearchParams
  *
+ * The values are kept percent-encoded so that they can be reused as-is by
+ * `convertToQueryString` (which does not re-encode). Iterating over
+ * `searchParams.entries()` would decode the values, and since
+ * `convertToQueryString` does not re-encode them, values containing
+ * reserved characters (`&`, `=`, `+`, spaces, ...) would corrupt the
+ * rebuilt query string.
+ *
  * @param searchParams
  * @returns
  */
 export function getQueryFromSearchParams(searchParams: URLSearchParams) {
-  return getQueryFromIterator(searchParams.entries());
+  const querystring = searchParams.toString();
+  if (querystring === "") return {};
+  return getQueryFromIterator(
+    querystring.split("&").map((part) => {
+      const [key, value] = part.split("=");
+      return [key, value] as const;
+    }),
+  );
 }
diff --git a/packages/tests-unit/tests/converters/utils.test.ts b/packages/tests-unit/tests/converters/utils.test.ts
index 9ca7b71bb..4241cae82 100644
--- a/packages/tests-unit/tests/converters/utils.test.ts
+++ b/packages/tests-unit/tests/converters/utils.test.ts
@@ -1,4 +1,7 @@
-import { removeUndefinedFromQuery } from "@opennextjs/aws/overrides/converters/utils.js";
+import {
+  getQueryFromSearchParams,
+  removeUndefinedFromQuery,
+} from "@opennextjs/aws/overrides/converters/utils.js";
 
 describe("removeUndefinedFromQuery", () => {
   it("should remove undefined from query", () => {
@@ -29,3 +32,43 @@ describe("removeUndefinedFromQuery", () => {
     expect(result).toEqual({});
   });
 });
+
+describe("getQueryFromSearchParams", () => {
+  it("returns an empty object when there are no params", () => {
+    expect(getQueryFromSearchParams(new URLSearchParams(""))).toEqual({});
+  });
+
+  it("returns a single param", () => {
+    expect(getQueryFromSearchParams(new URLSearchParams("key=value"))).toEqual({
+      key: "value",
+    });
+  });
+
+  it("groups repeated keys into an array", () => {
+    expect(
+      getQueryFromSearchParams(new URLSearchParams("key=value1&key=value2")),
+    ).toEqual({
+      key: ["value1", "value2"],
+    });
+  });
+
+  // https://github.com/opennextjs/opennextjs-cloudflare/issues/1134
+  it("keeps reserved characters percent-encoded so the value survives convertToQueryString", () => {
+    const raw =
+      "authorizationURL=https%3A%2F%2Fexample.com%2Fauth%3Fresponse_type%3Dcode%2Bid_token%26state%3Dabc&oauthState=xyz";
+    const query = getQueryFromSearchParams(new URLSearchParams(raw));
+
+    // The encoded value must be preserved (not decoded), otherwise the nested
+    // "&"/"="/"+"/space would break the rebuilt query string.
+    expect(query).toEqual({
+      authorizationURL:
+        "https%3A%2F%2Fexample.com%2Fauth%3Fresponse_type%3Dcode%2Bid_token%26state%3Dabc",
+      oauthState: "xyz",
+    });
+
+    // The value round-trips back to the original once decoded.
+    expect(decodeURIComponent(query.authorizationURL as string)).toBe(
+      "https://example.com/auth?response_type=code+id_token&state=abc",
+    );
+  });
+});