diff --git a/Source/control.cpp b/Source/control.cpp
index 4471bac09..a3192021b 100644
--- a/Source/control.cpp
+++ b/Source/control.cpp
@@ -231,6 +231,8 @@ void DrawSpell()
 
 	spl = plr[myplr]._pRSpell;
 	st = plr[myplr]._pRSplType;
+	
+	// BUGFIX: Move the next line into the if statement to avoid OOB (SPL_INVALID is -1)
 	tlvl = plr[myplr]._pISplLvlAdd + plr[myplr]._pSplLvl[spl];
 	if (st == RSPLTYPE_SPELL && spl != SPL_INVALID) {
 		if (!CheckSpell(myplr, spl, RSPLTYPE_SPELL, TRUE))
diff --git a/Source/monster.cpp b/Source/monster.cpp
index eeab1a85a..e3b7da66f 100644
--- a/Source/monster.cpp
+++ b/Source/monster.cpp
@@ -1215,6 +1215,7 @@ void M_CheckEFlag(int i)
 	}
 
 	f = 0;
+	// BUGFIX check (x > 0 && y < MAXDUNY)
 	m = dpiece_defs_map_2[x][y].mt;
 	if (m >= dpiece_defs_map_2[0][0].mt) {
 		for (j = 2; j < 10; j++) {
diff --git a/enums.h b/enums.h
index a939cd630..c1634a6ec 100644
--- a/enums.h
+++ b/enums.h
@@ -2158,7 +2158,7 @@ typedef enum spell_id {
 	SPL_HEALOTHER   = 0x22,
 	SPL_FLARE       = 0x23,
 	SPL_BONESPIRIT  = 0x24,
-	SPL_INVALID     = 0xFFFFFFFF,
+	SPL_INVALID     = -1,
 } spell_id;
 
 typedef enum _cmd_id {
@@ -2469,7 +2469,7 @@ typedef enum item_misc_id {
 	IMISC_MAPOFDOOM = 0x2A,
 	IMISC_EAR       = 0x2B,
 	IMISC_SPECELIX  = 0x2C,
-	IMISC_INVALID   = 0xFFFFFFFF,
+	IMISC_INVALID   = -1,
 } item_misc_id;
 
 typedef enum item_type {
@@ -2488,7 +2488,7 @@ typedef enum item_type {
 	ITYPE_RING   = 0xC,
 	ITYPE_AMULET = 0xD,
 	ITYPE_0E     = 0xE,
-	ITYPE_NONE   = 0xFFFFFFFF,
+	ITYPE_NONE   = -1,
 } item_type;
 
 typedef enum _item_indexes {
@@ -2557,7 +2557,7 @@ typedef enum quest_id {
 	QTYPE_PW      = 0xD,
 	QTYPE_BONE    = 0xE,
 	QTYPE_VB      = 0xF,
-	QTYPE_INVALID = 0xFFFFFFFF,
+	QTYPE_INVALID = -1,
 } quest_id;
 
 typedef enum quest_mush_state {