diff --git a/IPython/config/application.py b/IPython/config/application.py
index 8821456..32bde86 100644
--- a/IPython/config/application.py
+++ b/IPython/config/application.py
@@ -379,7 +379,7 @@ class Application(SingletonConfigurable):
         # Save a copy of the current config.
         newconfig = deepcopy(self.config)
         # Merge the new config into the current one.
-        newconfig._merge(config)
+        newconfig.merge(config)
         # Save the combined config as self.config, which triggers the traits
         # events.
         self.config = newconfig
diff --git a/IPython/config/configurable.py b/IPython/config/configurable.py
index 322ef06..18f465d 100644
--- a/IPython/config/configurable.py
+++ b/IPython/config/configurable.py
@@ -148,7 +148,7 @@ class Configurable(HasTraits):
         # Save a copy of the current config.
         newconfig = deepcopy(self.config)
         # Merge the new config into the current one.
-        newconfig._merge(config)
+        newconfig.merge(config)
         # Save the combined config as self.config, which triggers the traits
         # events.
         self.config = newconfig
diff --git a/IPython/config/loader.py b/IPython/config/loader.py
index 0fddae4..027253a 100644
--- a/IPython/config/loader.py
+++ b/IPython/config/loader.py
@@ -97,16 +97,21 @@ class Config(dict):
                     and isinstance(obj, dict) \
                     and not isinstance(obj, Config):
                 dict.__setattr__(self, key, Config(obj))
-
+    
     def _merge(self, other):
+        """deprecated alias, use Config.merge()"""
+        self.merge(other)
+    
+    def merge(self, other):
+        """merge another config object into this one"""
         to_update = {}
         for k, v in other.iteritems():
             if k not in self:
                 to_update[k] = v
             else: # I have this key
-                if isinstance(v, Config):
+                if isinstance(v, Config) and isinstance(self[k], Config):
                     # Recursively merge common sub Configs
-                    self[k]._merge(v)
+                    self[k].merge(v)
                 else:
                     # Plain updates for non-Configs
                     to_update[k] = v
@@ -328,7 +333,7 @@ class PyFileConfigLoader(FileConfigLoader):
                 # when a user s using a profile, but not the default config.
                 pass
             else:
-                self.config._merge(sub_config)
+                self.config.merge(sub_config)
 
         # Again, this needs to be a closure and should be used in config
         # files to get the config being loaded.
@@ -691,7 +696,7 @@ class KVArgParseConfigLoader(ArgParseConfigLoader):
         if self.extra_args:
             sub_parser = KeyValueConfigLoader()
             sub_parser.load_config(self.extra_args)
-            self.config._merge(sub_parser.config)
+            self.config.merge(sub_parser.config)
             self.extra_args = sub_parser.extra_args
 
 
@@ -715,5 +720,5 @@ def load_pyconfig_files(config_files, path):
         except:
             raise
         else:
-            config._merge(next_config)
+            config.merge(next_config)
     return config
diff --git a/IPython/config/tests/test_loader.py b/IPython/config/tests/test_loader.py
index d68334f..2d09f1d 100644
--- a/IPython/config/tests/test_loader.py
+++ b/IPython/config/tests/test_loader.py
@@ -222,11 +222,11 @@ class TestConfig(TestCase):
         c2 = Config()
         c2.bar = 10
         c2.Foo.bar = 10
-        c1._merge(c2)
+        c1.merge(c2)
         self.assertEqual(c1.Foo.bar, 10)
         self.assertEqual(c1.bar, 10)
         c2.Bar.bar = 10
-        c1._merge(c2)
+        c1.merge(c2)
         self.assertEqual(c1.Bar.bar, 10)
 
     def test_merge_exists(self):
@@ -236,12 +236,12 @@ class TestConfig(TestCase):
         c1.Foo.bam = 30
         c2.Foo.bar = 20
         c2.Foo.wow = 40
-        c1._merge(c2)
+        c1.merge(c2)
         self.assertEqual(c1.Foo.bam, 30)
         self.assertEqual(c1.Foo.bar, 20)
         self.assertEqual(c1.Foo.wow, 40)
         c2.Foo.Bam.bam = 10
-        c1._merge(c2)
+        c1.merge(c2)
         self.assertEqual(c1.Foo.Bam.bam, 10)
 
     def test_deepcopy(self):
@@ -267,17 +267,17 @@ class TestConfig(TestCase):
         self.assertEqual(c1.Foo.__class__, Config)
         self.assertEqual(c1.Foo.bar, 1)
     
-    def test_fromdict_merge(self):
+    def test_fromdictmerge(self):
         c1 = Config()
         c2 = Config({'Foo' : {'bar' : 1}})
-        c1._merge(c2)
+        c1.merge(c2)
         self.assertEqual(c1.Foo.__class__, Config)
         self.assertEqual(c1.Foo.bar, 1)
 
-    def test_fromdict_merge2(self):
+    def test_fromdictmerge2(self):
         c1 = Config({'Foo' : {'baz' : 2}})
         c2 = Config({'Foo' : {'bar' : 1}})
-        c1._merge(c2)
+        c1.merge(c2)
         self.assertEqual(c1.Foo.__class__, Config)
         self.assertEqual(c1.Foo.bar, 1)
         self.assertEqual(c1.Foo.baz, 2)