diff --git a/include/ap_expr.h b/include/ap_expr.h
index cccf42f092..bb26d2ac78 100644
--- a/include/ap_expr.h
+++ b/include/ap_expr.h
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include "httpd.h"
+
 /* conditional expression parser stuff */
 typedef enum {
     TOKEN_STRING,