diff --git a/lfs.h b/lfs.h
index 1f2804c8..ec603d00 100644
--- a/lfs.h
+++ b/lfs.h
@@ -94,6 +94,7 @@ typedef int32_t  lfsr_sdid_t;
 // valid positive return values
 enum lfs_error {
     LFS_ERR_OK          = 0,    // No error
+    LFS_ERR_UNKNOWN     = -1,   // Unknown error
     LFS_ERR_INVAL       = -22,  // Invalid parameter
     LFS_ERR_NOTSUP      = -95,  // Operation not supported
     LFS_ERR_IO          = -5,   // Error during device operation