diff --git a/a3/binary_search_tree.c b/a3/binary_search_tree.c
index 5528fa4..033d628 100644
--- a/a3/binary_search_tree.c
+++ b/a3/binary_search_tree.c
@@ -40,16 +40,16 @@ int *sorted_data(node_t *tree) {
             stack[stack_top++] = tree;
             tree = tree->left;
         }
-        
-        tree = stack[--stack_top];
-        sorted_array[index++] = tree->data;
 
-        tree = tree->right;
+        if (stack_top > 0) {
+            tree = stack[--stack_top];
+            sorted_array[index++] = tree->data;
+            tree = tree->right;
+        }
     }
 
     return sorted_array;
 }
-
 node_t *build_tree(int *tree_data, size_t tree_data_len) {
     if (tree_data == NULL || tree_data_len == 0) {
         return NULL;