Use ipairs instead of pairs since this is an indexed table.

diff --git a/Core.lua b/Core.lua
index 398a7b3..2d52572 100644
--- a/Core.lua
+++ b/Core.lua
@@ -990,7 +990,7 @@ do

 		local specialty = SpecialtyTable[current_prof]

-		for index, book_index in pairs(specialtices_indices) do
+		for index, book_index in ipairs(specialtices_indices) do
 			local spell_name = _G.GetSpellBookItemName(book_index, "profession")

 			if not spell_name then