diff --git a/programs/level.c b/programs/level.c
index 65b2f1c..fa6d10e 100644
--- a/programs/level.c
+++ b/programs/level.c
@@ -87,9 +87,9 @@ void drawTeleport(int16_t x, int16_t y, S3L_ScreenCoord size)
   int16_t halfSize = size / 2;
 
   S3L_ScreenCoord x0 = S3L_max(0,x - halfSize);
-  S3L_ScreenCoord x1 = S3L_min(S3L_RESOLUTION_X - 1,x + halfSize);
+  S3L_ScreenCoord x1 = S3L_min(S3L_RESOLUTION_X,x + halfSize);
   S3L_ScreenCoord y0 = S3L_max(0,y - halfSize);
-  S3L_ScreenCoord y1 = S3L_min(S3L_RESOLUTION_Y - 1,y + halfSize);
+  S3L_ScreenCoord y1 = S3L_min(S3L_RESOLUTION_Y,y + halfSize);
 
   for (S3L_ScreenCoord j = y0; j < y1; ++j)
     for (S3L_ScreenCoord i = x0; i < x1; ++i)
@@ -162,7 +162,10 @@ void draw()
 
   project3DPointToScreen(teleportPoint,scene.camera,&screenPoint);
 
-  if (screenPoint.z < S3L_zBufferRead(screenPoint.x,screenPoint.y)) 
+  if (screenPoint.w > 0 && 
+      screenPoint.x >= 0 && screenPoint.x <= S3L_RESOLUTION_X &&
+      screenPoint.y >= 0 && screenPoint.y <= S3L_RESOLUTION_Y &&
+      screenPoint.z < S3L_zBufferRead(screenPoint.x,screenPoint.y)) 
     drawTeleport(screenPoint.x,screenPoint.y,screenPoint.w);
 
   clock_t nowT = clock();
diff --git a/small3dlib.h b/small3dlib.h
index b553e7d..4044805 100644
--- a/small3dlib.h
+++ b/small3dlib.h
@@ -612,7 +612,12 @@ void S3L_newFrame();
 void S3L_zBufferClear();
 void S3L_stencilBufferClear();
 
+/** Writes a value (not necessarily depth! depends on the format of z-buffer)
+  to z-buffer (if enabled). Does NOT check boundaries! */
 void S3L_zBufferWrite(S3L_ScreenCoord x, S3L_ScreenCoord y, S3L_Unit value);
+
+/** Reads a value (not necessarily depth! depends on the format of z-buffer)
+  from z-buffer (if enabled). Does NOT check boundaries! */
 S3L_Unit S3L_zBufferRead(S3L_ScreenCoord x, S3L_ScreenCoord y);
 
 static inline void S3L_rotate2DPoint(S3L_Unit *x, S3L_Unit *y, S3L_Unit angle);
@@ -1465,7 +1470,7 @@ void project3DPointToScreen(
   result->z = point.z;
 
   result->w =
-    (point.z < 0) ? 0 :
+    (point.z <= 0) ? 0 :
     (
       (s * camera.focalLength * S3L_RESOLUTION_X) /
         (point.z * S3L_FRACTIONS_PER_UNIT)