diff --git a/fs_mgr/tools/dmuserd.cpp b/fs_mgr/tools/dmuserd.cpp
index 92f5878..e50a4a2 100644
--- a/fs_mgr/tools/dmuserd.cpp
+++ b/fs_mgr/tools/dmuserd.cpp
@@ -76,7 +76,7 @@
 
 static bool verbose = false;
 
-size_t write_all(int fd, void* buf, size_t len) {
+ssize_t write_all(int fd, void* buf, size_t len) {
     char* buf_c = (char*)buf;
     ssize_t total = 0;
     ssize_t once;
@@ -94,7 +94,7 @@
     return total;
 }
 
-size_t read_all(int fd, void* buf, size_t len) {
+ssize_t read_all(int fd, void* buf, size_t len) {
     char* buf_c = (char*)buf;
     ssize_t total = 0;
     ssize_t once;