diff --git a/game/modules/tome/class/Actor.lua b/game/modules/tome/class/Actor.lua
index 9ad1a16b59e9fec324eb909d883a2643d06390c0..bbce488522b4325e4617fbd104cb6062cf79f305 100644
--- a/game/modules/tome/class/Actor.lua
+++ b/game/modules/tome/class/Actor.lua
@@ -4870,7 +4870,7 @@ function _M:getTalentTypeMastery(tt, only_base)
 	local mastery = oldGetTalentTypeMastery(self, tt)
 	if only_base then return mastery end
 	local def = self:getTalentTypeFrom(tt)
-	local bonus1 = self.talents_mastery_bonus and self.talents_mastery_bonus[def.category] or 0
+	local bonus1 = def and self.talents_mastery_bonus and self.talents_mastery_bonus[def.category] or 0
 	local bonus2 = self.talents_mastery_bonus and self.talents_mastery_bonus.all or 0
 	return mastery + bonus1 + bonus2
 end