diff --git a/unix/syscall_linux.go b/unix/syscall_linux.go
index cb03b72..d251daf 100644
--- a/unix/syscall_linux.go
+++ b/unix/syscall_linux.go
@@ -2189,7 +2189,7 @@
 			gid = Getgid()
 		}
 
-		if uint32(gid) == st.Gid || isGroupMember(gid) {
+		if uint32(gid) == st.Gid || isGroupMember(int(st.Gid)) {
 			fmode = (st.Mode >> 3) & 7
 		} else {
 			fmode = st.Mode & 7