diff --git a/src/wayland-util.c b/src/wayland-util.c
index 7231346b..6936dad5 100644
--- a/src/wayland-util.c
+++ b/src/wayland-util.c
@@ -24,6 +24,7 @@
  * SOFTWARE.
  */
 
+#include <assert.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <stdint.h>
@@ -121,6 +122,8 @@ wl_array_add(struct wl_array *array, size_t size)
 		alloc *= 2;
 
 	if (array->alloc < alloc) {
+		assert(array->alloc > 0 || array->data == NULL);
+
 		if (array->alloc > 0)
 			data = realloc(array->data, alloc);
 		else