diff --git a/flang/include/flang/Parser/format-specification.h b/flang/include/flang/Parser/format-specification.h
index a34e68af2832f..28c8affd7bde0 100644
--- a/flang/include/flang/Parser/format-specification.h
+++ b/flang/include/flang/Parser/format-specification.h
@@ -18,6 +18,7 @@
 // dependences on other parts of the compiler's source code.
 // TODO: support Q formatting extension?
 
+#include "flang/Common/idioms.h"
 #include <cinttypes>
 #include <list>
 #include <optional>