diff --git a/src/ConfigMap.cpp b/src/ConfigMap.cpp
index 6bc988f..64ea32e 100644
--- a/src/ConfigMap.cpp
+++ b/src/ConfigMap.cpp
@@ -178,7 +178,7 @@ namespace configmaps
       return str.substr(front_idx, back_idx - front_idx + 1);
   }
 
-  bool ConfigMap::hasKey(std::string key)
+  bool ConfigMap::hasKey(std::string key) const
   {
     return (find(key) != end());
   }
diff --git a/src/ConfigMap.hpp b/src/ConfigMap.hpp
index 8c31b39..dc6f993 100644
--- a/src/ConfigMap.hpp
+++ b/src/ConfigMap.hpp
@@ -80,7 +80,7 @@ namespace configmaps {
       return w;
     }
 
-    bool hasKey(std::string key);
+    bool hasKey(std::string key) const;
     void updateMap(ConfigMap &update);
 
     static ConfigMap fromYamlStream(std::istream &in);