diff --git a/Secp256k1.xs b/Secp256k1.xs
index e8047ae..b6fc4f9 100644
--- a/Secp256k1.xs
+++ b/Secp256k1.xs
@@ -147,7 +147,7 @@ new(classname)
 
 		/* Blessing the object */
 		SV *secp_sv = newSViv(0);
-		RETVAL = sv_setref_iv(secp_sv, SvPVbyte_nolen(classname), (unsigned long) ctx);
+		RETVAL = sv_setref_iv(secp_sv, SvPVbyte_nolen(classname), (uintptr_t) ctx);
 		SvREADONLY_on(secp_sv);
 	OUTPUT:
 		RETVAL