diff --git a/include/boost/geometry/extensions/index/static_vector.hpp b/include/boost/geometry/extensions/index/static_vector.hpp
index 1de6829d7..e9180e81c 100644
--- a/include/boost/geometry/extensions/index/static_vector.hpp
+++ b/include/boost/geometry/extensions/index/static_vector.hpp
@@ -34,7 +34,7 @@ public:
     {}
 
     // strong
-    static_vector(size_type s)
+    explicit static_vector(size_type s)
         : m_size(0)
     {
         resize(s);                                                      // may throw