diff --git a/testsuite/rsa-keygen-test.c b/testsuite/rsa-keygen-test.c
index 6a3e687174bb6c9a6a17fd4e30258db18efc8dea..eff094f79ed7760d236a8ecb0afd6c46c0f56e1d 100644
--- a/testsuite/rsa-keygen-test.c
+++ b/testsuite/rsa-keygen-test.c
@@ -2,8 +2,14 @@
 
 #include "knuth-lfib.h"
 
+#if __GNUC__
+# define UNUSED __attribute__ ((__unused__))
+#else
+# define UNUSED
+#endif
+
 static void
-progress(void *ctx, int c)
+progress(void *ctx UNUSED, int c)
 {
   fputc(c, stderr);
 }