1 files changed, 3 insertions, 0 deletions
diff --git a/src/hash.hh b/src/hash.hh
index 509a27912a72..5ae5dc22aed8 100644
--- a/src/hash.hh
+++ b/src/hash.hh
@@ -22,6 +22,9 @@ struct Hash
     /* Check whether two hash are not equal. */
     bool operator != (Hash h2);
 
+    /* For sorting. */
+    bool operator < (const Hash & h) const;
+
     /* Convert a hash code into a hexadecimal representation. */
     operator string() const;
 };