diff --git a/java/com/google/gerrit/server/permissions/SectionSortCache.java b/java/com/google/gerrit/server/permissions/SectionSortCache.java
index c51bb80762..63f350fc61 100644
--- a/java/com/google/gerrit/server/permissions/SectionSortCache.java
+++ b/java/com/google/gerrit/server/permissions/SectionSortCache.java
@@ -31,7 +31,14 @@ import java.util.List;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** Caches the order AccessSections should be sorted for evaluation. */
+/**
+ * Caches the order AccessSections should be sorted for evaluation.
+ *
+ * <p>Access specifications for a more specific ref (eg. refs/heads/master rather than refs/heads/*)
+ * take precedence in ACL evaluations. So for each combination of (ref, list of access specs) we
+ * have to order the access specs by their distance from the ref to be matched. This is expensive,
+ * so cache the sorted ordering.
+ */
 @Singleton
 public class SectionSortCache {
   private static final Logger log = LoggerFactory.getLogger(SectionSortCache.class);