diff --git a/cxx/mount_astrom.h b/cxx/mount_astrom.h
index bf18880..e1f56cb 100644
--- a/cxx/mount_astrom.h
+++ b/cxx/mount_astrom.h
@@ -7,7 +7,6 @@
  *********************************/
 
 #include <chrono>
-#include <concepts>
 #include <xsimd/xsimd.hpp>