diff --git a/src/namedef.h b/src/namedef.h
index 17fa9e291..622e5ed5f 100644
--- a/src/namedef.h
+++ b/src/namedef.h
@@ -300,6 +300,7 @@ xx(ATan2)
 xx(VectorAngle)
 xx(Alpha)
 xx(Angle)
+xx(FlatAngle)
 xx(Args)
 xx(CeilingZ)
 xx(FloorZ)
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 77e862028..5dbfd9651 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -262,8 +262,11 @@ void AActor::Serialize(FArchive &arc)
 		<< projectilepassheight
 		<< Vel
 		<< tics
-		<< state
-		<< FlatAngle;
+		<< state;
+	if (SaveVersion >= 4545)
+	{
+		arc << FlatAngle;
+	}
 	if (arc.IsStoring())
 	{
 		int dmg;
diff --git a/src/thingdef/thingdef_data.cpp b/src/thingdef/thingdef_data.cpp
index 8b245e828..9669c78ab 100644
--- a/src/thingdef/thingdef_data.cpp
+++ b/src/thingdef/thingdef_data.cpp
@@ -627,6 +627,7 @@ void InitThingdef()
 	PType *array5 = NewArray(TypeSInt32, 5);
 	symt.AddSymbol(new PField(NAME_Alpha,		TypeFloat64,	VARF_Native, myoffsetof(AActor,Alpha)));
 	symt.AddSymbol(new PField(NAME_Angle,		TypeFloat64,	VARF_Native, myoffsetof(AActor,Angles.Yaw)));
+	symt.AddSymbol(new PField(NAME_FlatAngle,	TypeFloat64,	VARF_Native, myoffsetof(AActor,FlatAngle)));
 	symt.AddSymbol(new PField(NAME_Args,		array5,			VARF_Native, myoffsetof(AActor,args)));
 	symt.AddSymbol(new PField(NAME_CeilingZ,	TypeFloat64,	VARF_Native, myoffsetof(AActor,ceilingz)));
 	symt.AddSymbol(new PField(NAME_FloorZ,		TypeFloat64,	VARF_Native, myoffsetof(AActor,floorz)));
diff --git a/src/version.h b/src/version.h
index 68c7d0325..52b7ea0ba 100644
--- a/src/version.h
+++ b/src/version.h
@@ -72,7 +72,7 @@ const char *GetVersionString();
 // SAVESIG should match SAVEVER.
 
 // MINSAVEVER is the minimum level snapshot version that can be loaded.
-#define MINSAVEVER	4546
+#define MINSAVEVER	4545
 
 // Use 4500 as the base git save version, since it's higher than the
 // SVN revision ever got.