diff --git a/openssl-act-engine/src/engine_front.cpp b/openssl-act-engine/src/engine_front.cpp
index f6aa41a..14a7813 100644
--- a/openssl-act-engine/src/engine_front.cpp
+++ b/openssl-act-engine/src/engine_front.cpp
@@ -168,7 +168,7 @@ static int sct_rsa_sign(int type,
 
 static int sct_rsa_verify(int type,
 	const unsigned char *msg, unsigned int msglen,
-	unsigned char *signature, unsigned int siglen, const RSA *rsa)
+	const unsigned char *signature, unsigned int siglen, const RSA *rsa)
 {
 	CATCH_ALL(int,0,g_engine->rsa_verify(type, msg, msglen, signature, siglen, EXTRACT_CARD_KEY(rsa)));
 }