diff --git a/src/monger/errors.clj b/src/monger/result.clj
similarity index 54%
rename from src/monger/errors.clj
rename to src/monger/result.clj
index 250a881..83e3a5d 100644
--- a/src/monger/errors.clj
+++ b/src/monger/result.clj
@@ -7,8 +7,8 @@
 ;; the terms of this license.
 ;; You must not remove this notice, or any other, from this software.
 
-(ns monger.errors
-  (:import (com.mongodb DBObject WriteResult)
+(ns monger.result
+  (:import (com.mongodb DBObject BasicDBObject WriteResult CommandResult)
            (clojure.lang IPersistentMap))
   (:require [monger convertion]))
 
@@ -18,16 +18,25 @@
 ;;
 
 (defprotocol MongoCommandResult
-  (ok? [input] "Returns true if command result is a success"))
+  (ok?               [input] "Returns true if command result is a success")
+  (has-error?        [input] "Returns true if command result indicates an error")
+  (updated-existing? [input] "Returns true if command result has `updatedExisting` field set to true"))
 
 (extend-protocol MongoCommandResult
   DBObject
   (ok?
     [^DBObject result]
     (.contains [true "true" 1 1.0] (.get result "ok")))
+  (has-error?
+    [^DBObject result]
+    ;; yes, this is exactly the logic MongoDB Java driver uses.
+    (> (count (str (.get result "err"))) 0))
+
 
   WriteResult
   (ok?
     [^WriteResult result]
-    (ok? (.getLastError result))))
-
+    (and (not (nil? result)) (ok? (.getLastError result))))
+  (has-error?
+    [^WriteResult result]
+    (has-error? (.getLastError result))))
\ No newline at end of file
diff --git a/test/monger/test/errors.clj b/test/monger/test/errors.clj
deleted file mode 100644
index ed8d7c2..0000000
--- a/test/monger/test/errors.clj
+++ /dev/null
@@ -1,23 +0,0 @@
-(ns monger.test.errors
-  (:import (com.mongodb BasicDBObject WriteResult WriteConcern))
-  (:require [monger core collection convertion])
-  (:use [clojure.test]))
-
-
-;;
-;; MongoCommandResult
-;;
-
-
-(deftest test-ok?
-  (let [result-that-is-not-ok-1 (doto (BasicDBObject.) (.put "ok" 0))
-        result-that-is-not-ok-2 (doto (BasicDBObject.) (.put "ok" "false"))
-        result-that-is-ok-1     (doto (BasicDBObject.) (.put "ok" 1))
-        result-that-is-ok-2     (doto (BasicDBObject.) (.put "ok" "true"))
-        result-that-is-ok-3     (doto (BasicDBObject.) (.put "ok" 1.0))]
-    (is (not (monger.errors/ok? result-that-is-not-ok-1)))
-    (is (not (monger.errors/ok? result-that-is-not-ok-2)))
-    (is (monger.errors/ok? result-that-is-ok-1))
-    (is (monger.errors/ok? result-that-is-ok-2))
-    (is (monger.errors/ok? result-that-is-ok-3))))
-
diff --git a/test/monger/test/result.clj b/test/monger/test/result.clj
new file mode 100644
index 0000000..6225deb
--- /dev/null
+++ b/test/monger/test/result.clj
@@ -0,0 +1,31 @@
+(ns monger.test.result
+  (:import (com.mongodb BasicDBObject WriteResult WriteConcern))
+  (:require [monger core collection convertion])
+  (:use [clojure.test]))
+
+
+;;
+;; MongoCommandResult
+;;
+
+
+(deftest test-ok?
+  (let [result-that-is-not-ok-1 (doto (BasicDBObject.) (.put "ok" 0))
+        result-that-is-not-ok-2 (doto (BasicDBObject.) (.put "ok" "false"))
+        result-that-is-ok-1     (doto (BasicDBObject.) (.put "ok" 1))
+        result-that-is-ok-2     (doto (BasicDBObject.) (.put "ok" "true"))
+        result-that-is-ok-3     (doto (BasicDBObject.) (.put "ok" 1.0))]
+    (is (not (monger.result/ok? result-that-is-not-ok-1)))
+    (is (not (monger.result/ok? result-that-is-not-ok-2)))
+    (is (monger.result/ok? result-that-is-ok-1))
+    (is (monger.result/ok? result-that-is-ok-2))
+    (is (monger.result/ok? result-that-is-ok-3))))
+
+
+(deftest test-has-error?
+  (let [result-that-has-no-error1 (doto (BasicDBObject.) (.put "ok" 0))
+        result-that-has-no-error2 (doto (BasicDBObject.) (.put "err" ""))
+        result-that-has-error1    (doto (BasicDBObject.) (.put "err" (BasicDBObject.)))]
+        (is (not (monger.result/has-error? result-that-has-no-error1)))
+        (is (not (monger.result/has-error? result-that-has-no-error2)))
+        (is (monger.result/has-error?      result-that-has-error1))))