I observed today the following error in the bots, when running certain layout tests like the following one: 23:47:55.622 4977 worker/22 editing/selection/move-by-word-visually-single-space-inline-element.html output stderr lines: 23:47:55.622 4977 enchant_dict_check: assertion `g_utf8_validate(word, len, NULL)' failed 23:47:55.622 4977 enchant_dict_check: assertion `g_utf8_validate(word, len, NULL)' failed 23:47:55.623 4977 enchant_dict_check: assertion `g_utf8_validate(word, len, NULL)' failed 23:47:55.623 4977 enchant_dict_check: assertion `g_utf8_validate(word, len, NULL)' failed [...] << repeats some more times >> So, I briefly investigated the issue and it seems the problem is easily fixable by doing this: --- a/Source/WebCore/platform/text/gtk/TextCheckerEnchant.cpp +++ b/Source/WebCore/platform/text/gtk/TextCheckerEnchant.cpp @@ -115,7 +115,7 @@ void TextCheckerEnchant::checkSpellingOfString(const String& string, int& misspe g_utf8_strncpy(word.get(), cstart, wordLength); for (; dictIter != m_enchantDictionaries.end(); ++dictIter) { - if (enchant_dict_check(*dictIter, word.get(), wordLength)) { + if (enchant_dict_check(*dictIter, word.get(), bytes)) { misspellingLocation = start; misspellingLength = wordLength; } else { The explanation is that the 'length' parameter in enchant_dict_check accepts a number of bytes and not the number of utf8 characters, so it will fail in cases like this: word: דעפ => total characters: 3 / total bytes: 6 Thus, of course a call to enchant_dict_check with 3 as length will fail