diff --git a/src/ProjectFileIO.h b/src/ProjectFileIO.h
index 4af4a1a96..55f0883d1 100644
--- a/src/ProjectFileIO.h
+++ b/src/ProjectFileIO.h
@@ -14,6 +14,7 @@ Paul Licameli split from AudacityProject.h
 #include <atomic>
 #include <condition_variable>
 #include <memory>
+#include <map>
 #include <mutex>
 #include <thread>
 #include <set>