diff --git a/lib/date_to_str.c b/lib/date_to_str.c
index 67b99317..9d004d9e 100644
--- a/lib/date_to_str.c
+++ b/lib/date_to_str.c
@@ -26,6 +26,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <config.h>
+
 #include <string.h>
 #include <time.h>