diff --git a/uisimulator/common/io.c b/uisimulator/common/io.c
index cb8064c7d7..6335735f8f 100644
--- a/uisimulator/common/io.c
+++ b/uisimulator/common/io.c
@@ -227,7 +227,7 @@ int sim_rename(const char *oldpath, const char* newpath)
     return -1;
 }
 
-int sim_filesize(int fd)
+off_t sim_filesize(int fd)
 {
     int old = lseek(fd, 0, SEEK_CUR);
     int size = lseek(fd, 0, SEEK_END);