diff --git a/ext_tests.py b/ext_tests.py
index d7c7585..476f66d 100755
--- a/ext_tests.py
+++ b/ext_tests.py
@@ -94,7 +94,7 @@ def get_suite(filenames):
 
     for testfile in filenames:
         with open(testfile) as f:
-            tests = json.load(f)
+            tests = json.load(f, object_pairs_hook=jsonpatch.multidict)
             cls = make_test_case(tests)
             suite.addTest(unittest.makeSuite(cls))
 
diff --git a/jsonpatch.py b/jsonpatch.py
index bff1d50..7601248 100644
--- a/jsonpatch.py
+++ b/jsonpatch.py
@@ -43,6 +43,7 @@ __license__ = 'Modified BSD License'
 import copy
 import sys
 import operator
+import collections
 
 import json
 
@@ -70,6 +71,20 @@ class JsonPatchTestFailed(JsonPatchException, AssertionError):
     """ A Test operation failed """
 
 
+def multidict(ordered_pairs):
+    """Convert duplicate keys values to lists."""
+    # read all values into lists
+    d = collections.defaultdict(list)
+    for k, v in ordered_pairs:
+        d[k].append(v)
+
+    # unpack lists that have only 1 item
+    for k, v in d.items():
+        if len(v) == 1:
+            d[k] = v[0]
+    return dict(d)
+
+
 def apply_patch(doc, patch, in_place=False):
     """Apply list of patches to specified json document.
 
@@ -216,7 +231,7 @@ class JsonPatch(object):
 
         :return: :class:`JsonPatch` instance.
         """
-        patch = json.loads(patch_str)
+        patch = json.loads(patch_str, object_pairs_hook=multidict)
         return cls(patch)
 
     @classmethod
@@ -314,6 +329,10 @@ class JsonPatch(object):
             raise JsonPatchException("Operation does not contain 'op' member")
 
         op = operation['op']
+
+        if not isinstance(op, basestring):
+            raise JsonPatchException("Operation must be a string")
+
         if op not in self.operations:
             raise JsonPatchException("Unknown operation '%s'" % op)