@@ -164,11 +164,11 @@
 	BIO *p_bio;		/* Parent BIO (that is layered on Tcl_Channel) */
 
 	unsigned char *protos;	/* List of supported protocols in protocol format */
 	unsigned int protos_len; /* Length of protos */
 
-	char *err;
+	const char *err;
 } State;
 
 #ifdef USE_TCL_STUBS
 #ifndef Tcl_StackChannel
 #error "Unable to compile on this version of Tcl"