diff --git a/src/Makefile.am b/src/Makefile.am
index e97362f33eb191638728b48cd3383ca2ee305d77..2cea954ce896dc240fad72049bd1d2d62c9b0d90 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -9,7 +9,7 @@ lib_LTLIBRARIES =
 
 if ENABLE_CDI_LIB
   lib_LTLIBRARIES += libcdi.la
-  include_HEADERS += cdi.h cdi_datetime.h julian_date.h
+  include_HEADERS += cdi.h cdi_datetime.h julian_date.h calendar.h
 # add cdi.inc only if cfortran interface is required
 if USE_FC
   include_HEADERS += cdi.inc