diff --git a/packages/vite/src/node/utils.ts b/packages/vite/src/node/utils.ts
index 95b165ce0e8b73..e4a376ab7c7080 100644
--- a/packages/vite/src/node/utils.ts
+++ b/packages/vite/src/node/utils.ts
@@ -1197,7 +1197,7 @@ export const isNonDriveRelativeAbsolutePath = (p: string): boolean => {
 
 export function joinUrlSegments(a: string, b: string): string {
   if (!a || !b) {
-    return a + b
+    return a || b || ''
   }
   if (a.endsWith('/')) {
     a = a.substring(0, a.length - 1)