diff --git a/public/engine/IEngineTrace.h b/public/engine/IEngineTrace.h
index 5b02cadf..ec450b33 100644
--- a/public/engine/IEngineTrace.h
+++ b/public/engine/IEngineTrace.h
@@ -192,7 +192,7 @@ public:
 
 
 	//finds brushes in an AABB, prone to some false positives
-	virtual void GetBrushesInAABB( const Vector &vMins, const Vector &vMaxs, CBrushQuery *pQuery, int iContentsMask = 0xFFFFFFFF, int unknown ) = 0;
+	virtual void GetBrushesInAABB( const Vector &vMins, const Vector &vMaxs, CBrushQuery *pQuery, int iContentsMask = 0xFFFFFFFF, int unknown = 0 ) = 0;
 
 	//Creates a CPhysCollide out of all displacements wholly or partially contained in the specified AABB
 	virtual CPhysCollide* GetCollidableFromDisplacementsInAABB( const Vector& vMins, const Vector& vMaxs ) = 0;