diff --git a/dictsource/ar_rules b/dictsource/ar_rules
index e1188e2c..ed86ed84 100644
--- a/dictsource/ar_rules
+++ b/dictsource/ar_rules
@@ -51,6 +51,8 @@
 //C: ب پ ت ة ث ج ح خ د ذ ر ز س ش ص ض ط ظ ع غ ف ق ك ل م ن ئ ؤ ء أ آ إ ه
 // Consonant/vowel letters
 //B: ا و ي
+// "Thick" letters
+//F: ص ض ط ظ ق
 
 // all vowels/diphthongs in vocalized text
 // (fatha, damma, kasra, fatha+alef, fatha+alef_maksura, damma+waw, kasra+yeh, yeh+fatha, waw+fatha, superscript alef)