diff --git a/src/avl.c b/src/avl.c
index 4cb198daf..6a428cf24 100644
--- a/src/avl.c
+++ b/src/avl.c
@@ -205,6 +205,7 @@ void avl_free_nodes(avl_tree_t *avltree) {
         if(freeitem)
             freeitem(node->item);
         free(node);
+        node = NULL;
     }
     avl_clear_tree(avltree);
 }
@@ -218,6 +219,7 @@ void avl_free_nodes(avl_tree_t *avltree) {
 void avl_free_tree(avl_tree_t *avltree) {
     avl_free_nodes(avltree);
     free(avltree);
+    avltree = NULL;
 }
 
 static void avl_clear_node(avl_node_t *newnode) {
@@ -326,6 +328,7 @@ avl_node_t *avl_insert(avl_tree_t *avltree, void *item) {
         if(avl_insert_node(avltree, newnode))
             return newnode;
         free(newnode);
+        newnode = NULL;
         errno = EEXIST;
     }
     return NULL;
@@ -399,6 +402,7 @@ void *avl_delete_node(avl_tree_t *avltree, avl_node_t *avlnode) {
         if(avltree->freeitem)
             avltree->freeitem(item);
         free(avlnode);
+        avlnode = NULL;
     }
     return item;
 }
diff --git a/src/hv.c b/src/hv.c
index a7787b685..6ed4bb5b6 100644
--- a/src/hv.c
+++ b/src/hv.c
@@ -130,6 +130,7 @@ static dlnode_t * setup_cdllist(double *data, int d, int n) {
     }
 
     free(scratch);
+    scratch = NULL;
 
     for (i = 1; i <= n; i++)
         avl_init_node(head[i].tnode, head[i].x);
@@ -141,12 +142,12 @@ static dlnode_t * setup_cdllist(double *data, int d, int n) {
 }
 
 static void free_cdllist(dlnode_t * head) {
-    free(head->tnode); /* Frees _all_ nodes. */
-    free(head->next);
-    free(head->prev);
-    free(head->area);
-    free(head->vol);
-    free(head);
+    free(head->tnode); head->tnode = NULL;
+    free(head->next); head->next = NULL;
+    free(head->prev); head->prev = NULL;
+    free(head->area); head->area = NULL;
+    free(head->vol); head->vol = NULL;
+    free(head); head = NULL;
 }
 
 static void delete (dlnode_t *nodep, int dim, double * bound) {