diff --git a/lib/cm-impl.h b/lib/cm-impl.h
index c1da1594ed5ef6e4fe8c281d384c3ad7e5636e32..1cb755e55b3d4efa0cee82e537b1d93198dc7e22 100644
--- a/lib/cm-impl.h
+++ b/lib/cm-impl.h
@@ -31,6 +31,7 @@ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 #include <math.h>
 #include <ctype.h>
 #include <stdint.h>
+#include <stdarg.h>
 #ifdef WITH_MPI
 #include <unistd.h> /* for usleep */
 #include <mpi.h>