diff --git a/R/glmtree.R b/R/glmtree.R
index 0cdeca8..35c5d25 100644
--- a/R/glmtree.R
+++ b/R/glmtree.R
@@ -179,7 +179,7 @@ glmtree <-
       }
 
 
-      if (class(criterion_iter[[i]]) == "matrix") {
+      if (is(criterion_iter[[i]], "matrix")) {
         criterion_iter[[i]] <- normalizedGini(
           actual = criterion_iter[[i]][, 1],
           predicted = criterion_iter[[i]][, 2]