diff --git a/server/Makefile b/server/Makefile
index 1b62083..9d736b2 100644
--- a/server/Makefile
+++ b/server/Makefile
@@ -40,7 +40,7 @@ $(APP).p.native: $(wildcard *.ml) lwt_installed
 	$(OCAMLBUILD) $@
 
 lwt_installed:
-	opam install lwt
+	opam install camlp4 lwt
 
 run: all
 	./$(APP).native