diff --git a/chapter09/mixGaussPred.m b/chapter09/mixGaussPred.m
index ebebaa0..f614081 100644
--- a/chapter09/mixGaussPred.m
+++ b/chapter09/mixGaussPred.m
@@ -1,4 +1,4 @@
-function [label, R] = mixGaussPred(X, model)
+function [label, R] = mixGaussPred(model, X)
 % Predict label and responsibility for Gaussian mixture model.
 % Input:
 %   X: d x n data matrix
diff --git a/demo/ch09/mixGaussEm_demo.m b/demo/ch09/mixGaussEm_demo.m
index 95a14bb..a6ab295 100644
--- a/demo/ch09/mixGaussEm_demo.m
+++ b/demo/ch09/mixGaussEm_demo.m
@@ -16,6 +16,6 @@
 figure;
 plotClass(X1,z1);
 % predict
-z2 = mixGaussPred(X2,model);
+z2 = mixGaussPred(model,X2);
 figure;
 plotClass(X2,z2);
\ No newline at end of file