diff --git a/Source/inv.cpp b/Source/inv.cpp
index f70004eaa..cb10e2c08 100644
--- a/Source/inv.cpp
+++ b/Source/inv.cpp
@@ -1861,7 +1861,7 @@ void __fastcall RemoveInvItem(int pnum, int iv)
 	{
 		if ( plr[pnum]._pRSpell != SPL_INVALID )
 		{
-			// BUGFIX: Cast the literal `1` to `UINT64` to make that bitshift 64bit
+			// BUGFIX: Cast the literal `1` to `unsigned __int64` to make that bitshift 64bit
 			// this causes the last 4 skills to not reset correctly after use
 			if ( !(
 				plr[pnum]._pScrlSpells64
@@ -1885,7 +1885,7 @@ void __fastcall RemoveSpdBarItem(int pnum, int iv)
 	{
 		if ( plr[pnum]._pRSpell != SPL_INVALID )
 		{
-			// BUGFIX: Cast the literal `1` to `UINT64` to make that bitshift 64bit
+			// BUGFIX: Cast the literal `1` to `unsigned __int64` to make that bitshift 64bit
 			// this causes the last 4 skills to not reset correctly after use
 			if ( !(
 				plr[pnum]._pScrlSpells64
diff --git a/Source/items.cpp b/Source/items.cpp
index 313ce2853..12fbc9009 100644
--- a/Source/items.cpp
+++ b/Source/items.cpp
@@ -775,7 +775,7 @@ void __fastcall CalcPlrItemVals(int p, BOOL Loadgfx)
 	int dadd = 0; // added dexterity
 	int vadd = 0; // added vitality
 
-	UINT64 spl = 0; // bitarray for all enabled/active spells
+	unsigned __int64 spl = 0; // bitarray for all enabled/active spells
 
 	signed int fr = 0; // fire resistance
 	signed int lr = 0; // lightning resistance
@@ -938,7 +938,7 @@ void __fastcall CalcPlrItemVals(int p, BOOL Loadgfx)
 
 	// check if the current RSplType is a valid/allowed spell
 	if ( plr[p]._pRSplType == RSPLTYPE_CHARGES
-		&& !(spl & ((UINT64)1 << (plr[p]._pRSpell - 1))) )
+		&& !(spl & ((unsigned __int64)1 << (plr[p]._pRSpell - 1))) )
 	{
 		plr[p]._pRSpell = SPL_INVALID;
 		plr[p]._pRSplType = RSPLTYPE_INVALID;
diff --git a/Source/player.cpp b/Source/player.cpp
index eaa5d86b9..dac306b32 100644
--- a/Source/player.cpp
+++ b/Source/player.cpp
@@ -3105,7 +3105,7 @@ BOOL __fastcall PM_DoSpell(int pnum)
 		if ( !plr[pnum]._pSplFrom ) {
 			if ( plr[pnum]._pRSplType == RSPLTYPE_SCROLL) {
 				if ( !(plr[pnum]._pScrlSpells64
-					& (UINT64)1 << (plr[pnum]._pRSpell - 1))
+					& (unsigned __int64)1 << (plr[pnum]._pRSpell - 1))
 				) {
 					plr[pnum]._pRSpell = SPL_INVALID;
 					plr[pnum]._pRSplType = RSPLTYPE_INVALID;
@@ -3115,7 +3115,7 @@ BOOL __fastcall PM_DoSpell(int pnum)
 
 			if ( plr[pnum]._pRSplType == RSPLTYPE_CHARGES) {
 				if ( !(plr[pnum]._pISpells64
-					& (UINT64)1 << (plr[pnum]._pRSpell - 1))
+					& (unsigned __int64)1 << (plr[pnum]._pRSpell - 1))
 				) {
 					plr[pnum]._pRSpell = SPL_INVALID;
 					plr[pnum]._pRSplType = RSPLTYPE_INVALID;
diff --git a/structs.h b/structs.h
index 1da28b356..26180816e 100644
--- a/structs.h
+++ b/structs.h
@@ -213,15 +213,15 @@ struct PlayerStruct
 	char _pSBkSplType;
 	char _pSplLvl[64];
 	union {
-		__int64 _pMemSpells64;
+		unsigned __int64 _pMemSpells64;
 		int _pMemSpells[2];
 	};
 	union {
-		__int64 _pAblSpells64;
+		unsigned __int64 _pAblSpells64;
 		int _pAblSpells[2];
 	};
 	union {
-		__int64 _pScrlSpells64;
+		unsigned __int64 _pScrlSpells64;
 		int _pScrlSpells[2];
 	};
 	int _pSpellFlags;
@@ -322,7 +322,7 @@ struct PlayerStruct
 	int _pIBonusAC;
 	int _pIBonusDamMod;
 	union {
-		__int64 _pISpells64;
+		unsigned __int64 _pISpells64;
 		int _pISpells[2];
 	};
 	int _pIFlags;