diff --git a/src/Encrypt.c b/src/Encrypt.c
index f7f7059..8132572 100644
--- a/src/Encrypt.c
+++ b/src/Encrypt.c
@@ -176,7 +176,7 @@
 	return f;
 }
 
-bool _COSE_Enveloped_decrypt(COSE_Enveloped * pcose, COSE_RecipientInfo * pRecip, byte *pbKeyIn, size_t cbKeyIn, const char * szContext, cose_errback * perr)
+bool _COSE_Enveloped_decrypt(COSE_Enveloped * pcose, COSE_RecipientInfo * pRecip, const byte *pbKeyIn, size_t cbKeyIn, const char * szContext, cose_errback * perr)
 {
 	int alg;
 	const cn_cbor * cn = NULL;