diff --git a/src/unit_map.hpp b/src/unit_map.hpp
index a5366fa01cac..2a9e22ed2d11 100644
--- a/src/unit_map.hpp
+++ b/src/unit_map.hpp
@@ -228,7 +228,7 @@ class unit_map {
 
 		bool valid() const {
 			if(valid_for_dereference()) {
-				return bool (i_->second.unit);
+				return static_cast<bool> (i_->second.unit);
 			}
 			return false;
 		}