diff --git a/src/os.cpp b/src/os.cpp
index 8ab5007d80..e3d223325f 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -1350,7 +1350,7 @@ static void init_rand() {
         zig_panic("unable to open /dev/urandom");
     }
     char bytes[sizeof(unsigned)];
-    size_t amt_read;
+    ssize_t amt_read;
     while ((amt_read = read(fd, bytes, sizeof(unsigned))) == -1) {
         if (errno == EINTR) continue;
         zig_panic("unable to read /dev/urandom");