diff --git a/src/core/modules.c b/src/core/modules.c
index 38c33dea..a8860be6 100644
--- a/src/core/modules.c
+++ b/src/core/modules.c
@@ -28,7 +28,7 @@ static GHashTable *uniqids, *uniqstrids;
 static GHashTable *idlookup, *stridlookup;
 static int next_uniq_id;
 
-void *module_check_cast(void *object, int type_pos, const char *id)
+const void *module_check_cast(const void *object, int type_pos, const char *id)
 {
 	return object == NULL || module_find_id(id,
 		G_STRUCT_MEMBER(int, object, type_pos)) == -1 ? NULL : object;
diff --git a/src/core/modules.h b/src/core/modules.h
index 1e707c0c..9ae906b7 100644
--- a/src/core/modules.h
+++ b/src/core/modules.h
@@ -74,7 +74,7 @@ MODULE_FILE_REC *module_file_find(MODULE_REC *module, const char *name);
 #define MODULE_CHECK_CAST_MODULE(object, cast, type_field, module, id) \
 	((cast *) module_check_cast_module(object, \
 				offsetof(cast, type_field), module, id))
-void *module_check_cast(void *object, int type_pos, const char *id);
+const void *module_check_cast(const void *object, int type_pos, const char *id);
 void *module_check_cast_module(void *object, int type_pos,
 			       const char *module, const char *id);
 
diff --git a/src/core/recode.c b/src/core/recode.c
index 7185dd99..120d0783 100644
--- a/src/core/recode.c
+++ b/src/core/recode.c
@@ -25,6 +25,9 @@
 #include <irssi/src/lib-config/iconfig.h>
 #include <irssi/src/core/misc.h>
 
+#include <irssi/src/irc/core/irc.h>
+#include <irssi/src/irc/core/irc-servers.h>
+
 static char *translit_charset;
 static gboolean term_is_utf8;
 
@@ -65,6 +68,22 @@ static char *find_conversion(const SERVER_REC *server, const char *target)
 {
 	char *conv = NULL;
 
+	if (IS_IRC_SERVER(server))
+	{
+		IRC_SERVER_REC *irc_server = (IRC_SERVER_REC *) server;
+		if (g_hash_table_lookup(irc_server->isupport, "utf8only"))
+		{
+			/* "Clients implementing this specification MUST NOT send non-UTF-8
+			 * data to the server once they have seen this token."
+			 * "If a client implementing this specification sees this token,
+			 * they MUST set their outgoing encoding to UTF-8 without requiring
+			 * any user intervention."
+			 * -- https://ircv3.net/specs/extensions/utf8-only
+			 */
+			return NULL;
+		}
+	}
+
 	if (server != NULL && target != NULL) {
 		char *tagtarget = g_strdup_printf("%s/%s", server->tag, target);
 		conv = iconfig_get_str("conversions", tagtarget, NULL);