diff --git a/src/config.coffee b/src/config.coffee
index b7893087e..a0a2e27f0 100644
--- a/src/config.coffee
+++ b/src/config.coffee
@@ -352,7 +352,7 @@ class Config
     if args.length is 2
       # observe(keyPath, callback)
       [keyPath, callback, scopeDescriptor, options] = args
-    else if args.length is 3 and Array.isArray(scopeDescriptor)
+    else if args.length is 3 and (Array.isArray(scopeDescriptor) or scopeDescriptor instanceof ScopeDescriptor)
       # observe(scopeDescriptor, keyPath, callback)
       [scopeDescriptor, keyPath, callback, options] = args
     else if args.length is 3 and _.isString(scopeDescriptor) and _.isObject(keyPath)
diff --git a/src/tokenized-buffer.coffee b/src/tokenized-buffer.coffee
index 2e3691b32..fddbdc2e6 100644
--- a/src/tokenized-buffer.coffee
+++ b/src/tokenized-buffer.coffee
@@ -6,6 +6,7 @@ EmitterMixin = require('emissary').Emitter
 Serializable = require 'serializable'
 TokenizedLine = require './tokenized-line'
 Token = require './token'
+ScopeDescriptor = require './scope-descriptor'
 Grim = require 'grim'
 
 module.exports =
@@ -303,7 +304,7 @@ class TokenizedBuffer extends Model
       0
 
   scopeDescriptorForPosition: (position) ->
-    new ScopeDescriptor descriptor: @tokenForPosition(position).scopeDescriptor
+    new ScopeDescriptor(descriptor: @tokenForPosition(position).scopeDescriptor)
 
   tokenForPosition: (position) ->
     {row, column} = Point.fromObject(position)