diff --git a/src/nvim/marktree.h b/src/nvim/marktree.h
index 95d63dd14a..30f5aacebc 100644
--- a/src/nvim/marktree.h
+++ b/src/nvim/marktree.h
@@ -2,6 +2,7 @@
 #define NVIM_MARKTREE_H
 
 #include <stdint.h>
+#include <assert.h>
 
 #include "nvim/assert.h"
 #include "nvim/garray.h"