diff --git a/firmware/include/diacritic.h b/firmware/include/diacritic.h
index 5bc275ab9b..4d3390279c 100644
--- a/firmware/include/diacritic.h
+++ b/firmware/include/diacritic.h
@@ -22,5 +22,8 @@
 #define _DIACRITIC_H_
 #include "system.h"
 
+/* Tests whether a given charactor code is a diacritic mark
+ * Sets is_rtl if the character belongs to an RTL language
+ */
 int is_diacritic(const unsigned short char_code, bool *is_rtl);
 #endif