diff --git a/docs/DifferentiableProgramming.md b/docs/DifferentiableProgramming.md
index 4486e48f1d7d5..c40dd3da310ff 100644
--- a/docs/DifferentiableProgramming.md
+++ b/docs/DifferentiableProgramming.md
@@ -343,7 +343,7 @@ struct Observation {
 func meanError(for model: PodcastSpeedModel, _ observations: [Observation]) -> Float {
     var error: Float = 0
     for observation in observations {
-        error += abs(model.prediction(for: observation.state) - observation.userSpeed)
+        error += abs(model.prediction(for: observation.podcastState) - observation.userSpeed)
     }
     return error / Float(observations.count)
 }