diff --git a/.travis.yml b/.travis.yml
index d7a014d89..2f36aef48 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,6 +17,7 @@ addons:
       - valgrind
       - cppcheck
       - shellcheck
+      - iwyu
 os:
   - linux
 notifications:
diff --git a/src/economy.c b/src/economy.c
index 906019d3c..829b205a1 100644
--- a/src/economy.c
+++ b/src/economy.c
@@ -1989,7 +1989,7 @@ static void expandentertainment(region * r, econ_request *ecbegin, econ_request
     assert(total == 0);
 }
 
-int entertain_cmd(unit * u, struct order *ord, econ_request **io_req)
+static int entertain_cmd(unit * u, struct order *ord, econ_request **io_req)
 {
     region *r = u->region;
     int wants, max_e;