diff --git a/programs/pkey/rsa_verify.c b/programs/pkey/rsa_verify.c
index 94f0ef9..74030e4 100644
--- a/programs/pkey/rsa_verify.c
+++ b/programs/pkey/rsa_verify.c
@@ -59,7 +59,8 @@
 int main( int argc, char *argv[] )
 {
     FILE *f;
-    int ret = 1, c;
+    int ret = 1;
+    unsigned c;
     int exit_code = MBEDTLS_EXIT_FAILURE;
     size_t i;
     mbedtls_rsa_context rsa;