diff --git a/docs/changelogs/v4.7.7.md b/docs/changelogs/v4.7.7.md
index ac104dc1bb40..dc864f20d111 100644
--- a/docs/changelogs/v4.7.7.md
+++ b/docs/changelogs/v4.7.7.md
@@ -17,6 +17,7 @@ Release Date: Unreleased
 ## Bugs Fixed
 
 - **CORS:** Fixed a bug where `Cors::hasResponseHeaders()` matched header substrings via `str_contains()`, causing false positives when existing exposed headers shared a prefix with configured exposed headers.
+- **HTTP:** Fixed a bug where `SiteURIFactory::parseRequestURI()` truncated the query string to a single character when using query-based routing (`/?route?param=val`).
 - **HTTP:** Fixed a bug where `UploadedFile::move()` and `UploadedFile::store()` on Windows could store a file under a different name than `getName()` reported, or write its contents to an NTFS alternate data stream. Filenames ending in a period or space or containing a colon are now rejected, including explicitly supplied names.
 - **Security:** Fixed a bug where `Security::__construct()` threw a `TypeError` when the CSRF cookie was an array, causing an HTTP 500 response for affected requests.
 - **Worker Mode:** Fixed a bug where every request that ended with an uncaught exception, including a `404 Page Not Found` without a 404 override, called `exit()` in the exception handler. This ended the worker script, so FrankenPHP booted a new one, and the worker loop skipped its cleanup after the request. The exception handler now returns to the worker loop.
diff --git a/system/HTTP/SiteURIFactory.php b/system/HTTP/SiteURIFactory.php
index 3533b8383c6a..56fa6dacea6f 100644
--- a/system/HTTP/SiteURIFactory.php
+++ b/system/HTTP/SiteURIFactory.php
@@ -160,7 +160,7 @@ private function parseRequestURI(): string
         if (trim($path, '/') === '' && str_starts_with($query, '/')) {
             $parts    = explode('?', $query, 2);
             $path     = $parts[0];
-            $newQuery = $query[1] ?? '';
+            $newQuery = $parts[1] ?? '';
 
             $this->superglobals->setServer('QUERY_STRING', $newQuery);
         } else {
diff --git a/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php b/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php
index a61f19a2fefe..43a80e58d1e1 100644
--- a/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php
+++ b/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php
@@ -258,6 +258,73 @@ public function testQueryStringWithQueryString(): void
         $this->assertSame(['code' => 'good'], $_GET);
     }
 
+    public function testRequestURIWithQueryBasedRoutingAndQueryParameters(): void
+    {
+        // /index.php?/ci/woot?code=good#pos
+        service('superglobals')
+            ->setServer('REQUEST_URI', '/index.php?/ci/woot?code=good')
+            ->setServer('SCRIPT_NAME', '/index.php')
+            ->setGet('/ci/woot?code', 'good');
+
+        $factory = $this->createSiteURIFactory(service('superglobals')->getServerArray());
+
+        $expected = 'ci/woot';
+        $this->assertSame($expected, $factory->detectRoutePath('REQUEST_URI'));
+        $this->assertSame('code=good', $_SERVER['QUERY_STRING']); // @phpstan-ignore codeigniter.superglobalsOffsetAccess (checks the live superglobal, not the snapshot service)
+        $this->assertSame(['code' => 'good'], $_GET);
+    }
+
+    public function testRequestURIWithQueryBasedRoutingWithoutAdditionalQuery(): void
+    {
+        // /index.php?/ci/woot
+        service('superglobals')
+            ->setServer('REQUEST_URI', '/index.php?/ci/woot')
+            ->setServer('SCRIPT_NAME', '/index.php')
+            ->setGet('/ci/woot', '');
+
+        $factory = $this->createSiteURIFactory(service('superglobals')->getServerArray());
+
+        $expected = 'ci/woot';
+        $this->assertSame($expected, $factory->detectRoutePath('REQUEST_URI'));
+        $this->assertSame('', $_SERVER['QUERY_STRING']); // @phpstan-ignore codeigniter.superglobalsOffsetAccess (checks the live superglobal, not the snapshot service)
+        $this->assertSame([], $_GET);
+    }
+
+    public function testRequestURIWithQueryBasedRoutingPreservesSubsequentQuestionMarks(): void
+    {
+        // /index.php?/ci/woot?redirect=/a?b=1
+        service('superglobals')
+            ->setServer('REQUEST_URI', '/index.php?/ci/woot?redirect=/a?b=1')
+            ->setServer('SCRIPT_NAME', '/index.php')
+            ->setGet('/ci/woot?redirect', '/a?b=1');
+
+        $factory = $this->createSiteURIFactory(service('superglobals')->getServerArray());
+
+        $expected = 'ci/woot';
+        $this->assertSame($expected, $factory->detectRoutePath('REQUEST_URI'));
+        // Only the first '?' separates the path from the query string, so the
+        // remaining question marks must be kept inside the query string.
+        $this->assertSame('redirect=/a?b=1', $_SERVER['QUERY_STRING']); // @phpstan-ignore codeigniter.superglobalsOffsetAccess (checks the live superglobal, not the snapshot service)
+        $this->assertSame(['redirect' => '/a?b=1'], $_GET);
+    }
+
+    public function testRequestURIWithQueryBasedRoutingWithTrailingQuestionMark(): void
+    {
+        // /index.php?/ci/woot?
+        service('superglobals')
+            ->setServer('REQUEST_URI', '/index.php?/ci/woot?')
+            ->setServer('SCRIPT_NAME', '/index.php')
+            ->setGet('/ci/woot?', '');
+
+        $factory = $this->createSiteURIFactory(service('superglobals')->getServerArray());
+
+        $expected = 'ci/woot';
+        $this->assertSame($expected, $factory->detectRoutePath('REQUEST_URI'));
+        // A trailing '?' keeps an empty query string, not the '?' itself.
+        $this->assertSame('', $_SERVER['QUERY_STRING']); // @phpstan-ignore codeigniter.superglobalsOffsetAccess (checks the live superglobal, not the snapshot service)
+        $this->assertSame([], $_GET);
+    }
+
     public function testQueryStringRefreshesRequestWithoutOverwritingCustomValues(): void
     {
         if (! $this->effectiveRequestOrderIncludesGet()) {