diff --git a/src/addrman.h b/src/addrman.h
index 373b0f39f..2623d8980 100644
--- a/src/addrman.h
+++ b/src/addrman.h
@@ -458,7 +458,7 @@ public:
     }
 
     //! Return the number of (unique) addresses in all tables.
-    int size()
+    size_t size() const
     {
         return vRandom.size();
     }