diff --git a/src/p_actionfunctions.cpp b/src/p_actionfunctions.cpp
index 6ddfd5281..13a347ef2 100644
--- a/src/p_actionfunctions.cpp
+++ b/src/p_actionfunctions.cpp
@@ -6846,3 +6846,33 @@ DEFINE_ACTION_FUNCTION(AActor, A_CheckTerrain)
 	}
 	return 0;
 }
+
+DEFINE_ACTION_FUNCTION(AActor, A_SetSize)
+{
+	PARAM_SELF_PROLOGUE(AActor);
+	PARAM_FLOAT(newradius);
+	PARAM_FLOAT_DEF(newheight);
+	PARAM_BOOL_DEF(testpos);
+
+	if (newradius < 0.)		newradius = self->radius;
+	if (newheight < 0.)		newheight = self->Height;
+
+	double oldradius = self->radius;
+	double oldheight = self->Height;
+
+	self->UnlinkFromWorld();
+	self->radius = newradius;
+	self->Height = newheight;
+	self->LinkToWorld();
+
+	if (testpos && !P_TestMobjLocation(self))
+	{
+		self->UnlinkFromWorld();
+		self->radius = oldradius;
+		self->Height = oldheight;
+		self->LinkToWorld();
+		ACTION_RETURN_BOOL(false);
+	}
+
+	ACTION_RETURN_BOOL(true);
+}
diff --git a/src/scripting/codegeneration/codegen.cpp b/src/scripting/codegeneration/codegen.cpp
index 90fbcfe68..8e5750660 100644
--- a/src/scripting/codegeneration/codegen.cpp
+++ b/src/scripting/codegeneration/codegen.cpp
@@ -8955,7 +8955,7 @@ ExpEmit FxIfStatement::Emit(VMFunctionBuilder *build)
 	size_t jumpspot = ~0u;
 
 	TArray<size_t> yes, no;
-	Condition->EmitCompare(build, false, yes, no);
+	Condition->EmitCompare(build, WhenTrue == nullptr, yes, no);
 
 	if (WhenTrue != nullptr)
 	{
@@ -8964,11 +8964,14 @@ ExpEmit FxIfStatement::Emit(VMFunctionBuilder *build)
 	}
 	if (WhenFalse != nullptr)
 	{
-		if (!WhenTrue->CheckReturn()) jumpspot = build->Emit(OP_JMP, 0);	// no need to emit a jump if the block returns.
-		build->BackpatchListToHere(no);
+		if (WhenTrue != nullptr)
+		{
+			if (!WhenTrue->CheckReturn()) jumpspot = build->Emit(OP_JMP, 0);	// no need to emit a jump if the block returns.
+			build->BackpatchListToHere(no);
+		}
 		WhenFalse->EmitStatement(build);
 		if (jumpspot != ~0u) build->BackpatchToHere(jumpspot);
-		if (WhenTrue == nullptr) build->BackpatchListToHere(yes);
+		if (WhenTrue == nullptr) build->BackpatchListToHere(no);
 	}
 	else
 	{
diff --git a/wadsrc/static/zscript/actor.txt b/wadsrc/static/zscript/actor.txt
index d804a434c..0d264580a 100644
--- a/wadsrc/static/zscript/actor.txt
+++ b/wadsrc/static/zscript/actor.txt
@@ -793,6 +793,7 @@ class Actor : Thinker native
 	native bool A_CopySpriteFrame(int from, int to, int flags = 0);
 	native bool A_SetVisibleRotation(double anglestart = 0, double angleend = 0, double pitchstart = 0, double pitchend = 0, int flags = 0, int ptr = AAPTR_DEFAULT);
 	native void A_SetTranslation(name transname);
+	native bool A_SetSize(double newradius, double newheight = -1, bool testpos = false);
 
 	native void A_RearrangePointers(int newtarget, int newmaster = AAPTR_DEFAULT, int newtracer = AAPTR_DEFAULT, int flags=0);
 	native void A_TransferPointer(int ptr_source, int ptr_recepient, int sourcefield, int recepientfield=AAPTR_DEFAULT, int flags=0);