diff --git a/slides/cours_15.md b/slides/cours_15.md
index f72adb1a94929a279876bb2bf52ad8fe13da2ccb..b21a81888482add1e82c76293db9dc9ddc7f4a29 100644
--- a/slides/cours_15.md
+++ b/slides/cours_15.md
@@ -922,7 +922,7 @@ ajout(arbre, clé)
 tree_t position(tree_t tree, key_t key) {
     tree_t current = tree;
     if (NULL != current) {
-        subtree = key > current->key ? current->right :
+        tree_t subtree = key > current->key ? current->right :
         current->left;
         while (key != current->key && NULL != subtree) {
             current = subtree;