diff --git a/src/base/statistics.hh b/src/base/statistics.hh
index 3e1758a..404bdf1 100644
--- a/src/base/statistics.hh
+++ b/src/base/statistics.hh
@@ -2320,7 +2320,7 @@
     BinaryNode(NodePtr &a, NodePtr &b) : l(a), r(b) {}
 
     const VResult &
-    result() const
+    result() const override
     {
         Op op;
         const VResult &lvec = l->result();
@@ -2352,7 +2352,7 @@
     }
 
     Result
-    total() const
+    total() const override
     {
         const VResult &vec = this->result();
         const VResult &lvec = l->result();
@@ -2384,7 +2384,7 @@
     }
 
     size_type
-    size() const
+    size() const override
     {
         size_type ls = l->size();
         size_type rs = r->size();
@@ -2399,7 +2399,7 @@
     }
 
     std::string
-    str() const
+    str() const override
     {
         return csprintf("(%s %s %s)", l->str(), OpString<Op>::str(), r->str());
     }