From 609fdb7d26ceb0e2350db31af69ff311c2d371f7 Mon Sep 17 00:00:00 2001
From: Elliott Johnson <hello@ell.iott.dev>
Date: Tue, 27 Jan 2026 16:42:12 -0700
Subject: [PATCH] fix: only match rest params with matchers when the matcher
 matches

---
 .changeset/spotty-bears-doubt.md       |  5 +++++
 packages/kit/src/utils/routing.js      |  8 ++++++--
 packages/kit/src/utils/routing.spec.js | 20 ++++++++++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/spotty-bears-doubt.md

diff --git a/.changeset/spotty-bears-doubt.md b/.changeset/spotty-bears-doubt.md
new file mode 100644
index 000000000000..48fbcee1c7ca
--- /dev/null
+++ b/.changeset/spotty-bears-doubt.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: only match rest params with matchers when the matcher matches
diff --git a/packages/kit/src/utils/routing.js b/packages/kit/src/utils/routing.js
index f36988f370b8..ca8e9fc3b345 100644
--- a/packages/kit/src/utils/routing.js
+++ b/packages/kit/src/utils/routing.js
@@ -162,8 +162,12 @@ export function exec(match, params, matchers) {
 
 		// if `value` is undefined, it means this is an optional or rest parameter
 		if (value === undefined) {
-			if (param.rest) result[param.name] = '';
-			continue;
+			if (param.rest) {
+				// We need to allow the matcher to run so that it can decide if this optional rest param should be allowed to match
+				value = '';
+			} else {
+				continue;
+			}
 		}
 
 		if (!param.matcher || matchers[param.matcher](value)) {
diff --git a/packages/kit/src/utils/routing.spec.js b/packages/kit/src/utils/routing.spec.js
index 75f5487eb2fa..8434e83839ae 100644
--- a/packages/kit/src/utils/routing.spec.js
+++ b/packages/kit/src/utils/routing.spec.js
@@ -245,6 +245,26 @@ describe('exec', () => {
 			path: '/a/b/c',
 			expected: undefined
 		},
+		{
+			route: '/[...a=doesntmatch]/[b]',
+			path: '/foo',
+			expected: undefined
+		},
+		{
+			route: '/[...a=matches]/[b]',
+			path: '/foo',
+			expected: { a: '', b: 'foo' }
+		},
+		{
+			route: '/[...a=doesntmatch]/[b]/[c]',
+			path: '/foo/bar',
+			expected: undefined
+		},
+		{
+			route: '/[...a=matches]/[b]/[c]',
+			path: '/foo/bar',
+			expected: { a: '', b: 'foo', c: 'bar' }
+		},
 		{
 			route: '/[...catchall]',
 			path: '/\n',