diff --git a/oboformat/src/main/java/org/obolibrary/oboformat/model/Clause.java b/oboformat/src/main/java/org/obolibrary/oboformat/model/Clause.java
index 330d9a45fe..bf0ac447e1 100644
--- a/oboformat/src/main/java/org/obolibrary/oboformat/model/Clause.java
+++ b/oboformat/src/main/java/org/obolibrary/oboformat/model/Clause.java
@@ -99,8 +99,8 @@ void freezeXrefs() {
                 xrefs = Collections.singletonList(xref);
                 break;
             default:
-            if (values instanceof ArrayList) {
-                ((ArrayList) values).trimToSize();
+            if (xrefs instanceof ArrayList) {
+                ((ArrayList) xrefs).trimToSize();
             }
         }
     }