diff --git a/src/window.c b/src/window.c
index 8466c46..3937fc5 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4865,6 +4865,7 @@
     vim_free(wp->w_thumb_highlight);
     vim_free(wp->w_popup_title);
     list_unref(wp->w_popup_mask);
+    vim_free(wp->w_popup_mask_cells);
 #endif
 
 #ifdef FEAT_SYN_HL