diff --git a/src/main/java/com/justinsb/etcd/EtcdClient.java b/src/main/java/com/justinsb/etcd/EtcdClient.java
index babc363..a874dc4 100644
--- a/src/main/java/com/justinsb/etcd/EtcdClient.java
+++ b/src/main/java/com/justinsb/etcd/EtcdClient.java
@@ -145,6 +145,17 @@ public EtcdResult cas(String key, String prevValue, String value) throws EtcdCli
         return set0(key, data, new int[] { 200, 412 }, 101);
     }
 
+    /**
+     * Sets a key to a new value, depending on the previous existence of the key
+     */
+    public EtcdResult cas(String key, Boolean prevExist, String value) throws EtcdClientException {
+        List<BasicNameValuePair> data = Lists.newArrayList();
+        data.add(new BasicNameValuePair("value", value));
+        data.add(new BasicNameValuePair("prevExist", prevExist.toString()));
+
+        return set0(key, data, new int[] { 200, 201, 412 }, 105);
+    }
+
     /**
      * Watches the given subtree
      */
diff --git a/src/test/java/com/justinsb/etcd/SmokeTest.java b/src/test/java/com/justinsb/etcd/SmokeTest.java
index ee42189..a7ef699 100644
--- a/src/test/java/com/justinsb/etcd/SmokeTest.java
+++ b/src/test/java/com/justinsb/etcd/SmokeTest.java
@@ -136,6 +136,32 @@ public void testCAS() throws Exception {
 		Assert.assertEquals("world", result.node.value);
 	}
 
+	@Test
+	public void testCASPrevValue() throws Exception {
+		String key = prefix + "/cas";
+
+		EtcdResult result;
+
+		result = this.client.set(key, "hello");
+		result = this.client.get(key);
+		Assert.assertEquals("hello", result.node.value);
+
+		result = this.client.cas(key, false, "world");
+		Assert.assertEquals(true, result.isError());
+
+		result = this.client.get(key);
+		Assert.assertEquals("hello", result.node.value);
+
+		result = this.client.delete(key);
+		Assert.assertEquals(false, result.isError());
+
+		result = this.client.cas(key, false, "world");
+		Assert.assertEquals(false, result.isError());
+
+		result = this.client.get(key);
+		Assert.assertEquals("world", result.node.value);
+	}
+
 	@Test
 	public void testWatchPrefix() throws Exception {
 		String key = prefix + "/watch";