diff --git a/td/telegram/HashtagHints.cpp b/td/telegram/HashtagHints.cpp
index 3880e95c9..d2eccd076 100644
--- a/td/telegram/HashtagHints.cpp
+++ b/td/telegram/HashtagHints.cpp
@@ -13,6 +13,7 @@
 
 #include "td/utils/logging.h"
 #include "td/utils/tl_helpers.h"
+#include "td/utils/utf8.h"
 
 #include <functional>
 
@@ -73,6 +74,11 @@ string HashtagHints::get_key() const {
 }
 
 void HashtagHints::hashtag_used_impl(const string &hashtag) {
+  if (!check_utf8(hashtag)) {
+    LOG(ERROR) << "Trying to add invalid UTF-8 hashtag \"" << hashtag << '"';
+    return;
+  }
+
   // TODO: may be it should be optimized a little
   auto key = std::hash<std::string>()(hashtag);
   hints_.add(key, hashtag);
@@ -87,7 +93,7 @@ void HashtagHints::from_db(Result<string> data, bool dummy) {
   std::vector<string> hashtags;
   auto status = unserialize(hashtags, data.ok());
   if (status.is_error()) {
-    LOG(ERROR) << status;
+    LOG(ERROR) << "Failed to unserialize hashtag hints: " << status;
     return;
   }