diff --git a/include/privates.h b/include/privates.h
index e89c3e440..6e1cfa02e 100644
--- a/include/privates.h
+++ b/include/privates.h
@@ -15,6 +15,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <X11/Xdefs.h>
 #include <X11/Xosdefs.h>
 #include <X11/Xfuncproto.h>
+#include <assert.h>
 #include "misc.h"
 
 /*****************************************************************