diff --git a/lectures/tools/classification.md b/lectures/tools/classification.md
index 31dd6293..87075283 100644
--- a/lectures/tools/classification.md
+++ b/lectures/tools/classification.md
@@ -378,12 +378,12 @@ could be properly detected from noise (i.e. enemy aircraft vs. noise).
 def plot_roc(mod, X, y):
     # predicted_probs is an N x 2 array, where N is number of observations
     # and 2 is number of classes
-    predicted_probs = mod.predict_proba(X_test)
+    predicted_probs = mod.predict_proba(X)
 
     # keep the second column, for label=1
     predicted_prob1 = predicted_probs[:, 1]
 
-    fpr, tpr, _ = metrics.roc_curve(y_test, predicted_prob1)
+    fpr, tpr, _ = metrics.roc_curve(y, predicted_prob1)
 
     # Plot ROC curve
     fig, ax = plt.subplots()