diff --git a/dune/common/geometrytype.hh b/dune/common/geometrytype.hh
index 80de44bac3628dd16d392a91ad3323ced1dcdbba..0fedb5ee235003f54219d58f0dceacd120ee379a 100644
--- a/dune/common/geometrytype.hh
+++ b/dune/common/geometrytype.hh
@@ -105,7 +105,7 @@ namespace Dune {
      * \param t             Any object of type TopologyType. The object t itself is ignored.
      */
     template<class TopologyType>
-    GeometryType(TopologyType t)
+    explicit GeometryType(TopologyType t)
       : topologyId_(TopologyType::id), dim_(TopologyType::dimension), none_(false)
     {}