not really very happy about this

vcr/serialize.py

@@ -1,5 +1,6 @@
 from vcr.serializers import compat
 from vcr.request import Request
+import yaml
 
 #version 1 cassettes started with VCR 1.0.x.  Before 1.0.x, there was no versioning.
 CASSETTE_FORMAT_VERSION = 1 
@@ -16,15 +17,25 @@ Serializing: bytestring -> string (yaml persists to utf-8)
 Deserializing: string (yaml converts from utf-8) -> bytestring
 """
 
+def _looks_like_an_old_cassette(data):
+    return isinstance(data, list) and len(data) and 'request' in data[0]
+
+def _warn_about_old_cassette_format(data):
+    raise ValueError(
+        "Your cassette files were generated in an older version "
+        "of VCR. Delete your cassettes or run the migration script."
+        "See http://git.io/mHhLBg for more details."
+    )
 
 def deserialize(cassette_string, serializer):
-    data = serializer.deserialize(cassette_string)
-    if not isinstance(data, dict):
-        raise ValueError(
-            "Your cassette files were generated in an older version "
-            "of VCR. Delete your cassettes or run the migration script."
-            "See http://git.io/mHhLBg for more details."
-        )
+    try:
+        data = serializer.deserialize(cassette_string)
+    # Old cassettes used to use yaml object thingy so I have to
+    # check for some fairly stupid exceptions here
+    except (ImportError, yaml.constructor.ConstructorError):
+        _warn_about_old_cassette_format(data)
+    if _looks_like_an_old_cassette(data):
+        _warn_about_old_cassette_format(data)
 
     requests = [Request._from_dict(r['request']) for r in data['interactions']]
     responses = [compat.convert_to_bytes(r['response']) for r in data['interactions']]