diff --git a/.changeset/fix-vitest-base-path-conflict.md b/.changeset/fix-vitest-base-path-conflict.md
new file mode 100644
index 000000000000..d05cf1e1dd25
--- /dev/null
+++ b/.changeset/fix-vitest-base-path-conflict.md
@@ -0,0 +1,7 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: don't apply `paths.base` to Vite config when running under Vitest
+
+When `kit.paths.base` was set to a prefix of the project's filesystem path (e.g. `/Users`), Vite would strip that prefix from the URLs vite-node uses to fetch modules over HTTP, causing `ERR_MODULE_NOT_FOUND` failures. Under Vitest, `base` is now forced to `/` so module resolution works regardless of the configured base path.
diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index fe829e73e240..ccf6bf340c52 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -988,7 +988,12 @@ async function kit({ svelte_config }) {
 				} else {
 					new_config = {
 						appType: 'custom',
-						base: kit_paths_base,
+						// When running under Vitest, don't apply kit.paths.base — vite-node
+						// serves filesystem modules over HTTP and Vite will strip the base
+						// prefix from those URLs, breaking module resolution when the base
+						// happens to match the start of the project path (e.g. "/Users").
+						// See https://github.com/sveltejs/kit/issues/13737
+						base: process.env.VITEST ? '/' : kit_paths_base,
 						build: {
 							rollupOptions: {
 								// Vite dependency crawler needs an explicit JS entry point