diff --git a/src/thingdef/thingdef.h b/src/thingdef/thingdef.h
index e39d12ab0..08264e0a8 100644
--- a/src/thingdef/thingdef.h
+++ b/src/thingdef/thingdef.h
@@ -22,12 +22,15 @@ struct FFlagDef
 	unsigned int flagbit;
 	const char *name;
 	int structoffset;
+	int fieldsize;
 };
 
 FFlagDef *FindFlag (const PClass *type, const char *part1, const char *part2);
 void HandleDeprecatedFlags(AActor *defaults, FActorInfo *info, bool set, int index);
-bool CheckDeprecatedFlags(AActor *actor, FActorInfo *info, int index);
+bool CheckDeprecatedFlags(const AActor *actor, FActorInfo *info, int index);
 const char *GetFlagName(unsigned int flagnum, int flagoffset);
+void ModActorFlag(AActor *actor, FFlagDef *fd, bool set);
+INTBOOL CheckActorFlag(const AActor *actor, FFlagDef *fd);
 
 #define FLAG_NAME(flagnum, flagvar) GetFlagName(flagnum, myoffsetof(AActor, flagvar))
 
diff --git a/src/thingdef/thingdef_codeptr.cpp b/src/thingdef/thingdef_codeptr.cpp
index 304d57c07..7ed85a692 100644
--- a/src/thingdef/thingdef_codeptr.cpp
+++ b/src/thingdef/thingdef_codeptr.cpp
@@ -3629,14 +3629,7 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_ChangeFlag)
 			bool linkchange = flagp == &self->flags && (fd->flagbit == MF_NOBLOCKMAP || fd->flagbit == MF_NOSECTOR);
 
 			if (linkchange) self->UnlinkFromWorld();
-			if (expression)
-			{
-				*flagp |= fd->flagbit;
-			}
-			else
-			{
-				*flagp &= ~fd->flagbit;
-			}
+			ModActorFlag(self, fd, expression);
 			if (linkchange) self->LinkToWorld();
 		}
 		kill_after = self->CountsAsKill();
@@ -3721,13 +3714,7 @@ DEFINE_ACTION_FUNCTION_PARAMS(AActor, A_CheckFlag)
 
 	if (fd != NULL)
 	{
-		if (fd->structoffset == -1)
-		{
-			if (CheckDeprecatedFlags(owner, cls->ActorInfo, fd->flagbit)) {
-				ACTION_JUMP(jumpto);
-			}
-		}
-		else if ( fd->flagbit &  *(DWORD*)(((char*)owner) + fd->structoffset))
+		if (CheckActorFlag(owner, fd))
 		{
 			ACTION_JUMP(jumpto);
 		}
diff --git a/src/thingdef/thingdef_data.cpp b/src/thingdef/thingdef_data.cpp
index 301427ad4..3dbbacac0 100644
--- a/src/thingdef/thingdef_data.cpp
+++ b/src/thingdef/thingdef_data.cpp
@@ -55,10 +55,10 @@ static TArray<FVariableInfo*> variables;
 //==========================================================================
 
 // [RH] Keep GCC quiet by not using offsetof on Actor types.
-#define DEFINE_FLAG(prefix, name, type, variable) { prefix##_##name, #name, (int)(size_t)&((type*)1)->variable - 1 }
-#define DEFINE_FLAG2(symbol, name, type, variable) { symbol, #name, (int)(size_t)&((type*)1)->variable - 1 }
-#define DEFINE_DEPRECATED_FLAG(name) { DEPF_##name, #name, -1 }
-#define DEFINE_DUMMY_FLAG(name) { DEPF_UNUSED, #name, -1 }
+#define DEFINE_FLAG(prefix, name, type, variable) { prefix##_##name, #name, (int)(size_t)&((type*)1)->variable - 1, sizeof(((type *)0)->variable) }
+#define DEFINE_FLAG2(symbol, name, type, variable) { symbol, #name, (int)(size_t)&((type*)1)->variable - 1, sizeof(((type *)0)->variable) }
+#define DEFINE_DEPRECATED_FLAG(name) { DEPF_##name, #name, -1, 0 }
+#define DEFINE_DUMMY_FLAG(name) { DEPF_UNUSED, #name, -1, 0 }
 
 static FFlagDef ActorFlags[]=
 {
diff --git a/src/thingdef/thingdef_parse.cpp b/src/thingdef/thingdef_parse.cpp
index 11c000102..c065dfbe0 100644
--- a/src/thingdef/thingdef_parse.cpp
+++ b/src/thingdef/thingdef_parse.cpp
@@ -441,15 +441,7 @@ void HandleActorFlag(FScanner &sc, Baggage &bag, const char *part1, const char *
 		}
 		else
 		{
-			DWORD * flagvar = (DWORD*) ((char*)defaults + fd->structoffset);
-			if (mod == '+')
-			{
-				*flagvar |= fd->flagbit;
-			}
-			else
-			{
-				*flagvar &= ~fd->flagbit;
-			}
+			ModActorFlag(defaults, fd, mod == '+');
 		}
 	}
 	else
diff --git a/src/thingdef/thingdef_properties.cpp b/src/thingdef/thingdef_properties.cpp
index 482a841a2..e3461792b 100644
--- a/src/thingdef/thingdef_properties.cpp
+++ b/src/thingdef/thingdef_properties.cpp
@@ -95,6 +95,91 @@ static const PClass *FindClassTentative(const char *name, const char *ancestor)
 	return cls;
 }
 
+//==========================================================================
+//
+// Sets or clears a flag, taking field width into account.
+//
+//==========================================================================
+void ModActorFlag(AActor *actor, FFlagDef *fd, bool set)
+{
+	// Little-Endian machines only need one case, because all field sizes
+	// start at the same address. (Unless the machine has unaligned access
+	// exceptions, in which case you'll need multiple cases for it too.)
+#ifdef __BIG_ENDIAN__
+	if (fd->fieldsize == 4)
+#endif
+	{
+		DWORD *flagvar = (DWORD *)((char *)actor + fd->structoffset);
+		if (set)
+		{
+			*flagvar |= fd->flagbit;
+		}
+		else
+		{
+			*flagvar &= ~fd->flagbit;
+		}
+	}
+#ifdef __BIG_ENDIAN__
+	else if (fd->fieldsize == 2)
+	{
+		WORD *flagvar = (WORD *)((char *)actor + fd->structoffset);
+		if (set)
+		{
+			*flagvar |= fd->flagbit;
+		}
+		else
+		{
+			*flagvar &= ~fd->flagbit;
+		}
+	}
+	else
+	{
+		assert(fd->fieldsize == 1);
+		BYTE *flagvar = (BYTE *)((char *)actor + fd->structoffset);
+		if (set)
+		{
+			*flagvar |= fd->flagbit;
+		}
+		else
+		{
+			*flagvar &= ~fd->flagbit;
+		}
+	}
+#endif
+}
+
+//==========================================================================
+//
+// Returns whether an actor flag is true or not.
+//
+//==========================================================================
+
+INTBOOL CheckActorFlag(const AActor *owner, FFlagDef *fd)
+{
+	if (fd->structoffset == -1)
+	{
+		return CheckDeprecatedFlags(owner, owner->GetClass()->ActorInfo, fd->flagbit);
+	}
+	else
+#ifdef __BIG_ENDIAN__
+	if (fd->fieldsize == 4)
+#endif
+	{
+		return fd->flagbit & *(DWORD *)(((char*)owner) + fd->structoffset);
+	}
+#ifdef __BID_ENDIAN__
+	else if (fd->fieldsize == 2)
+	{
+		return fd->flagbit & *(WORD *)(((char*)owner) + fd->structoffset);
+	}
+	else
+	{
+		assert(fd->fieldsize == 1);
+		return fd->flagbit & *(BYTE *)(((char*)owner) + fd->structoffset);
+	}
+#endif
+}
+
 //===========================================================================
 //
 // HandleDeprecatedFlags
@@ -170,7 +255,7 @@ void HandleDeprecatedFlags(AActor *defaults, FActorInfo *info, bool set, int ind
 //
 //===========================================================================
 
-bool CheckDeprecatedFlags(AActor *actor, FActorInfo *info, int index)
+bool CheckDeprecatedFlags(const AActor *actor, FActorInfo *info, int index)
 {
 	// A deprecated flag is false if
 	// a) it hasn't been added here
@@ -211,11 +296,11 @@ bool CheckDeprecatedFlags(AActor *actor, FActorInfo *info, int index)
 		return (actor->BounceFlags & (BOUNCE_TypeMask|BOUNCE_UseSeeSound)) == BOUNCE_DoomCompat;
 
 	case DEPF_PICKUPFLASH:
-		return static_cast<AInventory*>(actor)->PickupFlash == PClass::FindClass("PickupFlash");
+		return static_cast<const AInventory*>(actor)->PickupFlash == PClass::FindClass("PickupFlash");
 		// A pure name lookup may or may not be more efficient, but I know no static identifier for PickupFlash.
 
 	case DEPF_INTERHUBSTRIP:
-		return !(static_cast<AInventory*>(actor)->InterHubAmount);
+		return !(static_cast<const AInventory*>(actor)->InterHubAmount);
 	}
 
 	return false; // Any entirely unknown flag is not set