diff --git a/lib/pyld/jsonld.py b/lib/pyld/jsonld.py
index ae27b9cc..fc3b8d4c 100755
--- a/lib/pyld/jsonld.py
+++ b/lib/pyld/jsonld.py
@@ -768,6 +768,8 @@ def expand(self, input_, options):
         options = options or {}
         options.setdefault('keepFreeFloatingNodes', False)
         options.setdefault('documentLoader', _default_document_loader)
+        options.setdefault('strict', False)
+        options.setdefault('droppedKeys', None)
 
         # if input is a string, attempt to dereference remote document
         if _is_string(input_):
@@ -1966,6 +1968,7 @@ def _expand(
             active_ctx, active_property, vocab=True)
 
         rval = {}
+        droppedKeys = options['droppedKeys']
         for key, value in sorted(element.items()):
             if key == '@context':
                 continue
@@ -1979,6 +1982,10 @@ def _expand(
                 not (
                     _is_absolute_iri(expanded_property) or
                     _is_keyword(expanded_property))):
+                if options['strict']:
+                    raise ValueError("Unrecognized key %s" % key)
+                elif droppedKeys is not None:
+                    droppedKeys.add(key)
                 continue
 
             if _is_keyword(expanded_property):
diff --git a/tests/test-issue50.py b/tests/test-issue50.py
new file mode 100644
index 00000000..5aed1ade
--- /dev/null
+++ b/tests/test-issue50.py
@@ -0,0 +1,54 @@
+import unittest
+
+import pyld.jsonld as jsonld
+
+class TestIssue50(unittest.TestCase):
+
+    CTX = { "foo": { "@id": "http://example.com/foo" } }
+    DATA = { "fooo": "bar" }
+    RESULT = []
+
+    def test_silently_ignored(self):
+        got = jsonld.expand(self.DATA,
+                            {'expandContext': self.CTX})
+        self.assertEqual(got, self.RESULT)
+
+    def test_strict_fails(self):
+        with self.assertRaises(ValueError):
+            got = jsonld.expand(self.DATA,
+                                {'expandContext': self.CTX, 'strict': True})
+
+    def test_dropped_keys(self):
+        dk = set()
+        got = jsonld.expand(self.DATA,
+                            {'expandContext': self.CTX, 'droppedKeys': dk})
+        self.assertEqual(got, self.RESULT)
+        self.assertSetEqual(dk, {"fooo"})
+
+
+    DATA2 = { "@id": "foo", "foo": "bar", "fooo": "baz", "http://example.com/other": "blah" }
+    RESULT2 = [{ "@id": u"foo",
+                 "http://example.com/foo": [{"@value": "bar"}],
+                 "http://example.com/other": [{"@value": "blah"}],
+    }]
+
+    def test_silently_ignored_2(self):
+        got = jsonld.expand(self.DATA2,
+                            {'expandContext': self.CTX})
+        self.assertEqual(got, self.RESULT2)
+
+    def test_strict_fails_2(self):
+        with self.assertRaises(ValueError):
+            got = jsonld.expand(self.DATA2,
+                                {'expandContext': self.CTX, 'strict': True})
+
+    def test_dropped_keys_2(self):
+        dk = set()
+        got = jsonld.expand(self.DATA2,
+                            {'expandContext': self.CTX, 'droppedKeys': dk})
+        self.assertEqual(got, self.RESULT2)
+        self.assertSetEqual(dk, {"fooo"})
+
+
+if __name__ == "__main__":
+    unittest.main()