diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index 12222c3db3c..e266207ee9e 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -36,6 +36,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <config.h>
 
+#include <stdarg.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>