diff --git a/README.macOS.md b/README.macOS.md
index 466c65aa2..ade1ba8e1 100644
--- a/README.macOS.md
+++ b/README.macOS.md
@@ -478,6 +478,7 @@ file is:
 
 ```bash
 cat << EOF > main.cxx
+  #include <FL/Fl.H>
   #include <FL/Fl_Window.H>
   int main(int argc, char **argv) {
     Fl_Window *win = new Fl_Window(600, 400, "Hello, world!");