diff --git a/getting-started/3-improving.md b/getting-started/3-improving.md
index 0568cc6..3114cd1 100644
--- a/getting-started/3-improving.md
+++ b/getting-started/3-improving.md
@@ -56,7 +56,7 @@ void main() {
     vec4 lightColor = texture(lightmap, lightCoord);
     
     // Calculate our new fog color!
-    float fogValue = vertexPosition < fogEnd ? smoothstep(fogStart, fogEnd, vertexPosition) : 1.0;
+    float fogValue = vertexDistance < fogEnd ? smoothstep(fogStart, fogEnd, vertexDistance) : 1.0;
 
     vec4 finalColor = texColor * lightColor * vertexColor;
     pixelColor = vec4(mix(finalColor.xyz, fogColor, fogValue), finalColor.a);
@@ -65,4 +65,4 @@ void main() {
 
 Note the use of the `mix` function, which mixes the first and second color based on the third value.
 
-Once you reload, you should now see you have border fog!
\ No newline at end of file
+Once you reload, you should now see you have border fog!