diff --git a/fs_mgr/tools/dmuserd.cpp b/fs_mgr/tools/dmuserd.cpp
index e50a4a2..6b68b28 100644
--- a/fs_mgr/tools/dmuserd.cpp
+++ b/fs_mgr/tools/dmuserd.cpp
@@ -81,7 +81,7 @@
     ssize_t total = 0;
     ssize_t once;
 
-    while (total < len) {
+    while (total < static_cast<ssize_t>(len)) {
         once = write(fd, buf_c + total, len - total);
         if (once < 0) return once;
         if (once == 0) {
@@ -99,7 +99,7 @@
     ssize_t total = 0;
     ssize_t once;
 
-    while (total < len) {
+    while (total < static_cast<ssize_t>(len)) {
         once = read(fd, buf_c + total, len - total);
         if (once < 0) return once;
         if (once == 0) {