diff --git a/src/vertex.c b/src/vertex.c
index 61e8472..4454872 100644
--- a/src/vertex.c
+++ b/src/vertex.c
@@ -41,6 +41,7 @@ void free_polygon(struct Vertex **head)
     }
 
     while(*head != NULL) {
+        // Double pointer so we can set the pointer itself to null.
         struct Vertex **temp = head;
         (*head) = (*head)->next;
         free(*temp);