diff --git a/test/unit/src/difficulty.cpp b/test/unit/src/difficulty.cpp
index 3dab73c..5a2f793 100644
--- a/test/unit/src/difficulty.cpp
+++ b/test/unit/src/difficulty.cpp
@@ -29,7 +29,7 @@ TEST(Difficulty, msa_features)
     double patterns_per_taxa = features->patterns_per_taxa;
     EXPECT_NEAR(patterns_per_taxa, n_patterns / (double)n_taxa, 0.001);
 
-    double patterns_per_site = features->patterns_per_taxa;
+    double patterns_per_site = features->patterns_per_site;
     EXPECT_NEAR(patterns_per_site, n_patterns / (double)n_sites, 0.001);
 
     double proportion_gaps = features->proportion_gaps;