diff --git a/src/p_actionfunctions.cpp b/src/p_actionfunctions.cpp
index 1a3333bdd5..0cb4e98493 100644
--- a/src/p_actionfunctions.cpp
+++ b/src/p_actionfunctions.cpp
@@ -6765,7 +6765,7 @@ DEFINE_ACTION_FUNCTION(AActor, A_CheckTerrain)
 DEFINE_ACTION_FUNCTION(AActor, A_SetSize)
 {
 	PARAM_SELF_PROLOGUE(AActor);
-	PARAM_FLOAT(newradius);
+	PARAM_FLOAT_DEF(newradius);
 	PARAM_FLOAT_DEF(newheight);
 	PARAM_BOOL_DEF(testpos);
 
diff --git a/wadsrc/static/zscript/actor.txt b/wadsrc/static/zscript/actor.txt
index a7f76f348f..bec97eda33 100644
--- a/wadsrc/static/zscript/actor.txt
+++ b/wadsrc/static/zscript/actor.txt
@@ -1145,7 +1145,7 @@ 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 bool A_SetSize(double newradius = -1, double newheight = -1, bool testpos = false);
 	native void A_SprayDecal(String name, double dist = 172);
 	native void A_SetMugshotState(String name);