diff --git a/simgear/props/props_test.cxx b/simgear/props/props_test.cxx
index b829df2e..a2b4e9e9 100644
--- a/simgear/props/props_test.cxx
+++ b/simgear/props/props_test.cxx
@@ -9,6 +9,7 @@
 
 #include <simgear/compiler.h>
 
+#include <memory>               // std::unique_ptr
 #include <iostream>
 #include <map>