diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 4e51f70e5..832ca33a5 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -43,7 +43,7 @@ std::atomic<int64_t> nTimeBestReceived(0); // Used only to inform the wallet of
 struct IteratorComparator
 {
     template<typename I>
-    bool operator()(const I& a, const I& b)
+    bool operator()(const I& a, const I& b) const
     {
         return &(*a) < &(*b);
     }