diff --git a/rdo.c b/rdo.c
index 80af53f..cd7be76 100644
--- a/rdo.c
+++ b/rdo.c
@@ -58,6 +58,9 @@ int main(int argc, char** argv) {
 		return 0;
 	}
 
+	if (geteuid() != 0)
+		errx(1, "The rdo binary needs to be installed as SUID.");
+
 	int ruid = getuid();
 	if (ruid == 0)
 		return runprog(argc, argv);