diff --git a/VolumeManager.cpp b/VolumeManager.cpp
index 071e027..c21eab3 100644
--- a/VolumeManager.cpp
+++ b/VolumeManager.cpp
@@ -1192,7 +1192,7 @@
         SLOGW("Attempt to unmount volume which isn't mounted (%d)\n",
              v->getState());
         errno = EBUSY;
-        return -1;
+        return UNMOUNT_NOT_MOUNTED_ERR;
     }
 
     cleanupAsec(v, force);