diff --git a/src/cryptoki.hxx b/src/cryptoki.hxx
index 0d734ba..99c0e94 100644
--- a/src/cryptoki.hxx
+++ b/src/cryptoki.hxx
@@ -2256,7 +2256,7 @@ namespace cryptoki {
       bool decryptinit(CK_MECHANISM_TYPE type, std::string param) {
         CRYPTOLOG("log");
         CK_MECHANISM mech = {
-          type, param.size()?&param[0]:0, param.size()
+          type, param.size()?&param[0]:0, (CK_ULONG)param.size()
         };
         CRYPTOLOG("decryptinit: type="<<type<<"; mech=("<<mech.mechanism
                      <<", "<<mech.pParameter<<", "<<mech.ulParameterLen<<')');
@@ -2487,7 +2487,7 @@ namespace cryptoki {
         CRYPTOLOG("log");
         CK_MECHANISM mech = {
           type, param.size()?const_cast<CK_VOID_PTR>((const void*)&param[0]):0,
-          param.size()
+          (CK_ULONG)param.size()
         };
         CRYPTOLOG("encryptinit: type="<<type<<"; mech=("<<mech.mechanism
                      <<", "<<mech.pParameter<<", "<<mech.ulParameterLen<<')');
@@ -2604,7 +2604,7 @@ namespace cryptoki {
       bool signinit(CK_MECHANISM_TYPE type, std::string param) {
         CRYPTOLOG("log");
         CK_MECHANISM mech = {
-          type, param.size()?&param[0]:0, param.size()
+          type, param.size()?&param[0]:0, (CK_ULONG)param.size()
         };
         CRYPTOLOG("signinit: type="<<type<<"; mech=("<<mech.mechanism
                      <<", "<<mech.pParameter<<", "<<mech.ulParameterLen<<')');
@@ -2639,7 +2639,7 @@ namespace cryptoki {
       bool verifyinit(CK_MECHANISM_TYPE type, std::string param) {
         CRYPTOLOG("log");
         CK_MECHANISM mech = {
-          type, param.size()?&param[0]:0, param.size()
+          type, param.size()?&param[0]:0, (CK_ULONG)param.size()
         };
         CRYPTOLOG("verifyinit: type="<<type<<"; mech=("<<mech.mechanism
                      <<", "<<mech.pParameter<<", "<<mech.ulParameterLen<<')');