diff --git a/src/main/java/edu/princeton/cs/algs4/BinarySearchST.java b/src/main/java/edu/princeton/cs/algs4/BinarySearchST.java
index bdb90a63e..cf98526b9 100644
--- a/src/main/java/edu/princeton/cs/algs4/BinarySearchST.java
+++ b/src/main/java/edu/princeton/cs/algs4/BinarySearchST.java
@@ -313,6 +313,7 @@ public Key select(int k) {
      */
     public Key floor(Key key) {
         if (key == null) throw new IllegalArgumentException("argument to floor() is null"); 
+        if (isEmpty()) throw new NoSuchElementException("called floor() with empty symbol table");
         int i = rank(key);
         if (i < n && key.compareTo(keys[i]) == 0) return keys[i];
         if (i == 0) return null;
@@ -329,6 +330,7 @@ public Key floor(Key key) {
      */
     public Key ceiling(Key key) {
         if (key == null) throw new IllegalArgumentException("argument to ceiling() is null"); 
+        if (isEmpty()) throw new NoSuchElementException("called ceiling() with empty symbol table");
         int i = rank(key);
         if (i == n) return null; 
         else return keys[i];