diff --git a/daemon.py b/daemon.py
index 2d1ec172..ca8ed0b1 100644
--- a/daemon.py
+++ b/daemon.py
@@ -1079,6 +1079,8 @@ class PubServer(BaseHTTPRequestHandler):
         elif self.headers.get('content-length'):
             headersDict['content-length'] = self.headers['content-length']
 
+        originalMessageJson = messageJson.copy()
+
         # For follow activities add a 'to' field, which is a copy
         # of the object field
         messageJson, toFieldExists = \
@@ -1097,7 +1099,7 @@ class PubServer(BaseHTTPRequestHandler):
                                  self.server.httpPrefix,
                                  nickname,
                                  self.server.domainFull,
-                                 messageJson,
+                                 messageJson, originalMessageJson,
                                  messageBytesDecoded,
                                  headersDict,
                                  self.path,
diff --git a/inbox.py b/inbox.py
index d0c35733..37a476dc 100644
--- a/inbox.py
+++ b/inbox.py
@@ -313,6 +313,7 @@ def inboxPermittedMessage(domain: str, messageJson: {},
 def savePostToInboxQueue(baseDir: str, httpPrefix: str,
                          nickname: str, domain: str,
                          postJsonObject: {},
+                         originalPostJsonObject: {},
                          messageBytes: str,
                          httpHeaders: {},
                          postPath: str, debug: bool) -> str:
@@ -437,6 +438,7 @@ def savePostToInboxQueue(baseDir: str, httpPrefix: str,
         'httpHeaders': httpHeaders,
         'path': postPath,
         'post': postJsonObject,
+        'original': originalPostJsonObject,
         'digest': digest,
         'filename': filename,
         'destination': destination
@@ -2703,24 +2705,30 @@ def runInboxQueue(recentPostsCache: {}, maxRecentPosts: int,
         if debug:
             print('DEBUG: http header signature check success')
 
-        if not queueJson['post'].get('signature'):
-            print('WARN: jsonld inbox signature signature missing from ' +
-                  keyId)
-#        else:
-#            if not jsonldVerify(queueJson['post'], pubKey):
-#                hasJsonSig = False
-#                if debug:
-#                    print('**************************************')
-#                    print('WARN: jsonld signature check failed ' +
-#                          str(queueJson['post']))
-#                    print('--------------------------------------')
-#                    print(keyId)
-#                    print(pubKey)
-#                    print('**************************************')
-#            else:
-#                if debug:
-#                    print('jsonld inbox signature check success')
-#
+        # should the json signature be checked?
+        checkJsonSignature = False
+        if queueJson['original'].get('@context'):
+            checkJsonSignature = True
+            if not queueJson['original'].get('signature'):
+                print('WARN: jsonld inbox signature signature missing from ' +
+                      keyId)
+                checkJsonSignature = False
+
+        # check json signature
+        if checkJsonSignature:
+            # use the original json message received, not one which may have
+            # been modified along the way
+            if not jsonldVerify(queueJson['original'], pubKey):
+                print('WARN: jsonld signature check failed ' +
+                      keyId + ' ' + pubKey + ' ' +
+                      str(queueJson['original']))
+                if os.path.isfile(queueFilename):
+                    os.remove(queueFilename)
+                if len(queue) > 0:
+                    queue.pop(0)
+                continue
+            else:
+                print('jsonld inbox signature check success')
 
         # set the id to the same as the post filename
         # This makes the filename and the id consistent
diff --git a/jsonldsig.py b/jsonldsig.py
index 30a09e96..df7e93a5 100644
--- a/jsonldsig.py
+++ b/jsonldsig.py
@@ -116,6 +116,9 @@ def jsonldSign(jldDocument: {}, privateKeyPem: str) -> {}:
     """
     Produces a signed JSON-LD document with a Json Web Signature
     """
+    if not jldDocument.get('@context'):
+        print('WARN: json document must have @context to sign')
+        return jldDocument
     jldDocument = deepcopy(jldDocument)
     normalizedJldHash = _jsonldNormalize(jldDocument)
     jwsSignature = _signJws(normalizedJldHash, privateKeyPem)
@@ -135,6 +138,11 @@ def jsonldVerify(signedJldDocument: {}, publicKeyPem: str) -> bool:
     """
     Verifies the Json Web Signature of a signed JSON-LD Document
     """
+    if not isinstance(signedJldDocument, dict):
+        return False
+    if not signedJldDocument.get('@context'):
+        print('json document must have @context')
+        return False
     signedJldDocument = deepcopy(signedJldDocument)
     signature = signedJldDocument.pop('signature')
     jwsSignature = signature['signatureValue'].encode('utf-8')
diff --git a/pyjsonld.py b/pyjsonld.py
index f0f55b41..5f31ca0e 100644
--- a/pyjsonld.py
+++ b/pyjsonld.py
@@ -234,7 +234,7 @@ def link(input_, ctx, options=None):
     return frame(input, frame, options)
 
 
-def normalize(input_, options=None):
+def normalize(input_: {}, options=None):
     """
     Performs JSON-LD normalization.
 
@@ -1016,6 +1016,13 @@ class JsonLdProcessor(object):
                 'Could not convert input to RDF dataset before normalization.',
                 'jsonld.NormalizeError', cause=cause)
 
+        # check that the data is not empty
+        if '@default' in dataset:
+            if not dataset['@default']:
+                raise JsonLdError(
+                    'Could not convert input to RDF dataset.',
+                    'jsonld.NormalizeError', cause=None)
+
         # do normalization
         return self._normalize(dataset, options)
 
diff --git a/tests.py b/tests.py
index 70421cd3..bc900348 100644
--- a/tests.py
+++ b/tests.py
@@ -1978,6 +1978,7 @@ def testRemoveTextFormatting():
 def testJsonld():
     print("testJsonld")
     jldDocument = {
+        "@context": "https://www.w3.org/ns/activitystreams",
         "description": "My json document",
         "numberField": 83582,
         "object": {
@@ -2031,10 +2032,11 @@ def testJsonld():
     assert(signedDocument['signature']['type'] == 'RsaSignatureSuite2017')
     assert(jsonldVerify(signedDocument, publicKeyPem))
     # alter the signed document
-    # signedDocument['object']['content'] = 'forged content'
-    # assert(not jsonldVerify(signedDocument, publicKeyPem))
+    signedDocument['object']['content'] = 'forged content'
+    assert(not jsonldVerify(signedDocument, publicKeyPem))
 
     jldDocument2 = {
+        "@context": "https://www.w3.org/ns/activitystreams",
         "description": "Another json document",
         "numberField": 13353,
         "object": {
@@ -2049,8 +2051,8 @@ def testJsonld():
     if signedDocument['signature']['signatureValue'] == \
        signedDocument2['signature']['signatureValue']:
         print('json signature has not changed for different documents')
-#    assert(signedDocument['signature']['signatureValue'] !=
-#           signedDocument2['signature']['signatureValue'])
+    assert(signedDocument['signature']['signatureValue'] !=
+           signedDocument2['signature']['signatureValue'])
 
 
 def testSiteIsActive():