diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ebd7682..5b4bc50 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,7 +29,7 @@ jobs:
 
     env:
       PROJECT: "collisionhook"
-      SDKS: "css hl2dm dods tf2"
+      SDKS: "css hl2dm dods tf2 l4d l4d2"
       MMSOURCE_VERSION: "1.11"
       SOURCEMOD_VERSION: "1.11"
       CACHE_PATH: ${{ github.workspace }}/cache
@@ -103,12 +103,7 @@ jobs:
           # Verify github cache, and see if we don't have the sdks already cloned and update them
           for sdk in ${{ env.SDKS }}
           do
-              # TODO: remove these conditionals once https://github.com/alliedmodders/hl2sdk/pull/198 is merged
-              if [ "${sdk}" == "tf2" ]; then
-                shallow_checkout "https://github.com/Kenzzer/hl2sdk" "tf2_win64" "hl2sdk-tf2"
-              else
-                shallow_checkout "https://github.com/alliedmodders/hl2sdk" "${sdk}" "hl2sdk-${sdk}"
-              fi
+              shallow_checkout "https://github.com/alliedmodders/hl2sdk" "${sdk}" "hl2sdk-${sdk}"
           done
 
           shallow_checkout "https://github.com/alliedmodders/ambuild" "master" "ambuild"
diff --git a/src/extension.cpp b/src/extension.cpp
index a809bd9..bc64a3e 100644
--- a/src/extension.cpp
+++ b/src/extension.cpp
@@ -22,7 +22,11 @@ SMEXT_LINK( &g_CollisionHook );
 
 SH_DECL_HOOK0( IPhysics, CreateEnvironment, SH_NOATTRIB, 0 , IPhysicsEnvironment * );
 SH_DECL_HOOK1_void( IPhysicsEnvironment, SetCollisionSolver, SH_NOATTRIB, 0, IPhysicsCollisionSolver * );
+#if SOURCE_ENGINE == SE_LEFT4DEAD2
+SH_DECL_HOOK6( IPhysicsCollisionSolver, ShouldCollide, SH_NOATTRIB, 0, int, IPhysicsObject *, IPhysicsObject *, void *, void *, const PhysicsCollisionRulesCache_t &, const PhysicsCollisionRulesCache_t & );
+#else
 SH_DECL_HOOK4( IPhysicsCollisionSolver, ShouldCollide, SH_NOATTRIB, 0, int, IPhysicsObject *, IPhysicsObject *, void *, void * );
+#endif
 
 
 IGameConfig *g_pGameConf = NULL;
@@ -175,7 +179,11 @@ void CollisionHook::SetCollisionSolver( IPhysicsCollisionSolver *pSolver )
 	RETURN_META( MRES_IGNORED );
 }
 
+#if SOURCE_ENGINE == SE_LEFT4DEAD2
+int CollisionHook::VPhysics_ShouldCollide( IPhysicsObject *pObj1, IPhysicsObject *pObj2, void *pGameData1, void *pGameData2, const PhysicsCollisionRulesCache_t &objCache1, const PhysicsCollisionRulesCache_t &obhCache2 )
+#else
 int CollisionHook::VPhysics_ShouldCollide( IPhysicsObject *pObj1, IPhysicsObject *pObj2, void *pGameData1, void *pGameData2 )
+#endif
 {
 	if ( g_pCollisionFwd->GetFunctionCount() == 0 )
 		RETURN_META_VALUE( MRES_IGNORED, 1 ); // no plugins are interested, let the game decide
diff --git a/src/extension.h b/src/extension.h
index d7aaefe..ff8e568 100644
--- a/src/extension.h
+++ b/src/extension.h
@@ -9,6 +9,9 @@
 class IPhysicsEnvironment;
 class IPhysicsCollisionSolver;
 class IPhysicsObject;
+#if SOURCE_ENGINE == SE_LEFT4DEAD2
+struct PhysicsCollisionRulesCache_t;
+#endif
 
 
 class CollisionHook :
@@ -87,17 +90,21 @@ public:
 public: // hooks
 	IPhysicsEnvironment *CreateEnvironment();
 	void SetCollisionSolver( IPhysicsCollisionSolver *pSolver );
+#if SOURCE_ENGINE == SE_LEFT4DEAD2
+	int VPhysics_ShouldCollide( IPhysicsObject *pObj1, IPhysicsObject *pObj2, void *pGameData1, void *pGameData2, const PhysicsCollisionRulesCache_t &objCache1, const PhysicsCollisionRulesCache_t &objCache2 );
+#else
 	int VPhysics_ShouldCollide( IPhysicsObject *pObj1, IPhysicsObject *pObj2, void *pGameData1, void *pGameData2 );
+#endif
 
 };
 
 // adapted from util_shared.h
-inline const CBaseEntity *UTIL_EntityFromEntityHandle( const IHandleEntity *pConstHandleEntity )
-{
-	IHandleEntity *pHandleEntity = const_cast<IHandleEntity *>( pConstHandleEntity );
-	IServerUnknown *pUnk = static_cast<IServerUnknown *>( pHandleEntity );
-
-	return pUnk->GetBaseEntity();
+inline const CBaseEntity *UTIL_EntityFromEntityHandle( const IHandleEntity *pConstHandleEntity )
+{
+	IHandleEntity *pHandleEntity = const_cast<IHandleEntity *>( pConstHandleEntity );
+	IServerUnknown *pUnk = static_cast<IServerUnknown *>( pHandleEntity );
+
+	return pUnk->GetBaseEntity();
 }