Index: generic/tls.c
==================================================================
--- generic/tls.c
+++ generic/tls.c
@@ -982,46 +982,46 @@
     ERR_clear_error();
 
     switch ((enum protocol)index) {
 	case TLS_SSL2:
 #if OPENSSL_VERSION_NUMBER >= 0x10100000L || defined(NO_SSL2) || defined(OPENSSL_NO_SSL2)
-	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", NULL);
+	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", (char *) NULL);
 	    return TCL_ERROR;
 #else
 	    method = SSLv2_method(); break;
 #endif
 	case TLS_SSL3:
 #if defined(NO_SSL3) || defined(OPENSSL_NO_SSL3) || defined(OPENSSL_NO_SSL3_METHOD)
-	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", NULL);
+	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", (char *) NULL);
 	    return TCL_ERROR;
 #else
 	    method = SSLv3_method(); break;
 #endif
 	case TLS_TLS1:
 #if defined(NO_TLS1) || defined(OPENSSL_NO_TLS1) || defined(OPENSSL_NO_TLS1_METHOD)
-	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", NULL);
+	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", (char *) NULL);
 	    return TCL_ERROR;
 #else
 	    method = TLSv1_method(); break;
 #endif
 	case TLS_TLS1_1:
 #if defined(NO_TLS1_1) || defined(OPENSSL_NO_TLS1_1) || defined(OPENSSL_NO_TLS1_1_METHOD)
-	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", NULL);
+	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", (char *) NULL);
 	    return TCL_ERROR;
 #else
 	    method = TLSv1_1_method(); break;
 #endif
 	case TLS_TLS1_2:
 #if defined(NO_TLS1_2) || defined(OPENSSL_NO_TLS1_2) || defined(OPENSSL_NO_TLS1_2_METHOD)
-	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", NULL);
+	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", (char *) NULL);
 	    return TCL_ERROR;
 #else
 	    method = TLSv1_2_method(); break;
 #endif
 	case TLS_TLS1_3:
 #if defined(NO_TLS1_3) || defined(OPENSSL_NO_TLS1_3)
-	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", NULL);
+	    Tcl_AppendResult(interp, protocols[index], ": protocol not supported", (char *) NULL);
 	    return TCL_ERROR;
 #else
 	    method = TLS_method();
 	    SSL_CTX_set_min_proto_version(ctx, TLS1_3_VERSION);
 	    SSL_CTX_set_max_proto_version(ctx, TLS1_3_VERSION);
@@ -1032,17 +1032,17 @@
 	    break;
     }
 
     ctx = SSL_CTX_new(method);
     if (ctx == NULL) {
-	Tcl_AppendResult(interp, GET_ERR_REASON(), NULL);
+	Tcl_AppendResult(interp, GET_ERR_REASON(), (char *) NULL);
 	return TCL_ERROR;
     }
 
     ssl = SSL_new(ctx);
     if (ssl == NULL) {
-	Tcl_AppendResult(interp, GET_ERR_REASON(), NULL);
+	Tcl_AppendResult(interp, GET_ERR_REASON(), (char *) NULL);
 	SSL_CTX_free(ctx);
 	return TCL_ERROR;
     }
 
     /* Use list and order as would be sent in a ClientHello or all available ciphers */
@@ -1185,11 +1185,11 @@
 
     /* Make sure to operate on the topmost channel */
     chan = Tcl_GetTopChannel(chan);
     if (Tcl_GetChannelType(chan) != Tls_ChannelType()) {
 	Tcl_AppendResult(interp, "bad channel \"", Tcl_GetChannelName(chan),
-	    "\": not a TLS channel", NULL);
+	    "\": not a TLS channel", (char *) NULL);
 	Tcl_SetErrorCode(interp, "TLS", "HANDSHAKE", "CHANNEL", "INVALID", (char *) NULL);
 	return(TCL_ERROR);
     }
     statePtr = (State *)Tcl_GetChannelInstanceData(chan);
 
@@ -1422,11 +1422,11 @@
 	 * Make sure to operate on the topmost channel
 	 */
 	chan = Tcl_GetTopChannel(chan);
 	if (Tcl_GetChannelType(chan) != Tls_ChannelType()) {
 	    Tcl_AppendResult(interp, "bad channel \"", Tcl_GetChannelName(chan),
-		"\": not a TLS channel", NULL);
+		"\": not a TLS channel", (char *) NULL);
 	    Tcl_SetErrorCode(interp, "TLS", "IMPORT", "CHANNEL", "INVALID", (char *) NULL);
 	    Tls_Free((char *) statePtr);
 	    return TCL_ERROR;
 	}
 	ctx = ((State *)Tcl_GetChannelInstanceData(chan))->ctx;
@@ -1689,11 +1689,11 @@
     /* Make sure to operate on the topmost channel */
     chan = Tcl_GetTopChannel(chan);
 
     if (Tcl_GetChannelType(chan) != Tls_ChannelType()) {
 	Tcl_AppendResult(interp, "bad channel \"", Tcl_GetChannelName(chan),
-		"\": not a TLS channel", NULL);
+		"\": not a TLS channel", (char *) NULL);
 	    Tcl_SetErrorCode(interp, "TLS", "UNIMPORT", "CHANNEL", "INVALID", (char *) NULL);
 	return TCL_ERROR;
     }
 
     if (Tcl_UnstackChannel(interp, chan) == TCL_ERROR) {
@@ -2107,11 +2107,11 @@
 
     /* Make sure to operate on the topmost channel */
     chan = Tcl_GetTopChannel(chan);
     if (Tcl_GetChannelType(chan) != Tls_ChannelType()) {
 	Tcl_AppendResult(interp, "bad channel \"", Tcl_GetChannelName(chan),
-		"\": not a TLS channel", NULL);
+		"\": not a TLS channel", (char *) NULL);
 	Tcl_SetErrorCode(interp, "TLS", "STATUS", "CHANNEL", "INVALID", (char *) NULL);
 	return TCL_ERROR;
     }
     statePtr = (State *) Tcl_GetChannelInstanceData(chan);
 
@@ -2226,11 +2226,11 @@
 
     /* Make sure to operate on the topmost channel */
     chan = Tcl_GetTopChannel(chan);
     if (Tcl_GetChannelType(chan) != Tls_ChannelType()) {
 	Tcl_AppendResult(interp, "bad channel \"", Tcl_GetChannelName(chan),
-	    "\": not a TLS channel", NULL);
+	    "\": not a TLS channel", (char *) NULL);
 	Tcl_SetErrorCode(interp, "TLS", "CONNECTION", "CHANNEL", "INVALID", (char *) NULL);
 	return(TCL_ERROR);
     }
 
     objPtr = Tcl_NewListObj(0, NULL);