diff --git a/Source/control.cpp b/Source/control.cpp
index 8b7220a69..487a0fcee 100644
--- a/Source/control.cpp
+++ b/Source/control.cpp
@@ -2464,8 +2464,8 @@ void CheckSBook()
 	unsigned __int64 spl;
 
 	if (MouseX >= RIGHT_PANEL + 11 && MouseX < RIGHT_PANEL + 48 && MouseY >= 18 && MouseY < 314) {
-		spl = plr[myplr]._pMemSpells | plr[myplr]._pISpells | plr[myplr]._pAblSpells;
 		sn = SpellPages[sbooktab][(MouseY - 18) / 43];
+		spl = plr[myplr]._pMemSpells | plr[myplr]._pISpells | plr[myplr]._pAblSpells;
 		if (sn != -1 && spl & (__int64)1 << (sn - 1)) {
 			st = RSPLTYPE_SPELL;
 			if (plr[myplr]._pISpells & (__int64)1 << (sn - 1)) {