diff --git a/lib/core/mergeConfig.js b/lib/core/mergeConfig.js
index ad7d0f8..1da9040 100644
--- a/lib/core/mergeConfig.js
+++ b/lib/core/mergeConfig.js
@@ -16,18 +16,20 @@ module.exports = function mergeConfig(config1, config2) {
   var config = {};
 
   utils.forEach(['url', 'method', 'params', 'data'], function valueFromConfig2(prop) {
-    config[prop] = config2[prop];
+    if (typeof config2[prop] !== 'undefined') {
+      config[prop] = config2[prop];
+    }
   });
 
-  utils.forEach(['headers', 'auth', 'proxy'], function mergeValues(prop) {
-    if (typeof config2[prop] !== 'undefined') {
-      if (typeof config2[prop] === 'object') {
-        config[prop] = utils.deepMerge(config1[prop], config2[prop]);
-      } else {
-        config[prop] = config2[prop];
-      }
-    } else if (typeof config1[prop] !== 'undefined') {
+  utils.forEach(['headers', 'auth', 'proxy'], function mergeDeepProperties(prop) {
+    if (utils.isObject(config2[prop])) {
+      config[prop] = utils.deepMerge(config1[prop], config2[prop]);
+    } else if (typeof config2[prop] !== 'undefined') {
+      config[prop] = config2[prop];
+    } else if (utils.isObject(config1[prop])) {
       config[prop] = utils.deepMerge(config1[prop]);
+    } else if (typeof config1[prop] !== 'undefined') {
+      config[prop] = config1[prop];
     }
   });
 
@@ -37,7 +39,11 @@ module.exports = function mergeConfig(config1, config2) {
     'xsrfHeaderName', 'onUploadProgress', 'onDownloadProgress', 'maxContentLength',
     'validateStatus', 'maxRedirects', 'httpAgent', 'httpsAgent', 'cancelToken'
   ], function defaultToConfig2(prop) {
-    config[prop] = typeof config2[prop] === 'undefined' ? config1[prop] : config2[prop];
+    if (typeof config2[prop] !== 'undefined') {
+      config[prop] = config2[prop];
+    } else if (typeof config1[prop] !== 'undefined') {
+      config[prop] = config1[prop];
+    }
   });
 
   return config;
diff --git a/lib/defaults.js b/lib/defaults.js
index e1bc1ca..65a25d5 100644
--- a/lib/defaults.js
+++ b/lib/defaults.js
@@ -26,7 +26,6 @@ function getDefaultAdapter() {
 }
 
 var defaults = {
-  method: 'get',
   adapter: getDefaultAdapter(),
 
   transformRequest: [function transformRequest(data, headers) {
diff --git a/test/specs/core/mergeConfig.spec.js b/test/specs/core/mergeConfig.spec.js
new file mode 100644
index 0000000..bf6d209
--- /dev/null
+++ b/test/specs/core/mergeConfig.spec.js
@@ -0,0 +1,69 @@
+var defaults = require('../../../lib/defaults');
+var mergeConfig = require('../../../lib/core/mergeConfig');
+
+describe('core::mergeConfig', function() {
+  it('should accept undefined for second argument', function() {
+    expect(mergeConfig(defaults, undefined)).toEqual(defaults);
+  });
+
+  it('should accept an object for second argument', function() {
+    expect(mergeConfig(defaults, {})).toEqual(defaults);
+  });
+
+  it('should not leave references', function() {
+    var merged = mergeConfig(defaults, {});
+    expect(merged).not.toBe(defaults);
+    expect(merged.headers).not.toBe(defaults.headers);
+  });
+
+  it('should allow setting request options', function() {
+    var config = {
+      url: '__sample url__',
+      method: '__sample method__',
+      params: '__sample params__',
+      data: { foo: true }
+    };
+    var merged = mergeConfig(defaults, config);
+    expect(merged.url).toEqual(config.url);
+    expect(merged.method).toEqual(config.method);
+    expect(merged.params).toEqual(config.params);
+    expect(merged.data).toEqual(config.data);
+  });
+
+  it('should not inherit request options', function() {
+    var localDefaults = {
+      url: '__sample url__',
+      method: '__sample method__',
+      params: '__sample params__',
+      data: { foo: true }
+    };
+    var merged = mergeConfig(localDefaults, {});
+    expect(merged.url).toEqual(undefined);
+    expect(merged.method).toEqual(undefined);
+    expect(merged.params).toEqual(undefined);
+    expect(merged.data).toEqual(undefined);
+  });
+
+  it('should merge auth, headers, proxy with defaults', function() {
+    expect(mergeConfig({ auth: undefined }, { auth: { user: 'foo', pass: 'test' } })).toEqual({
+      auth: { user: 'foo', pass: 'test' }
+    });
+    expect(mergeConfig({ auth: { user: 'foo', pass: 'test' } }, { auth: { pass: 'foobar' } })).toEqual({
+      auth: { user: 'foo', pass: 'foobar' }
+    });
+  });
+
+  it('should overwrite auth, headers, proxy with a non-object value', function() {
+    expect(mergeConfig({ auth: { user: 'foo', pass: 'test' } }, { auth: false })).toEqual({
+      auth: false
+    });
+    expect(mergeConfig({ auth: { user: 'foo', pass: 'test' } }, { auth: null })).toEqual({
+      auth: null
+    });
+  });
+
+  it('should allow setting other options', function() {
+    var merged = mergeConfig(defaults, { timeout: 123 });
+    expect(merged.timeout).toEqual(123);
+  });
+});