diff --git a/src/v3/apiInject.ts b/src/v3/apiInject.ts
index 76928268b13..1ad27a9fe14 100644
--- a/src/v3/apiInject.ts
+++ b/src/v3/apiInject.ts
@@ -66,6 +66,7 @@ export function inject(
       warn(`injection "${String(key)}" not found.`)
     }
   } else if (__DEV__) {
-    warn(`inject() can only be used inside setup() or functional components.`)
+    const keyName = key ? String(key) : 'unknown'
+    warn(`inject(${keyName}) can only be used inside setup() or functional components.`)
   }
-}
+}