diff --git a/lib/ex-mode.coffee b/lib/ex-mode.coffee
index 5274e0a..c627483 100644
--- a/lib/ex-mode.coffee
+++ b/lib/ex-mode.coffee
@@ -50,3 +50,8 @@ module.exports = ExMode =
       description: 'when splitting, split from right'
       type: 'boolean'
       default: 'false'
+    gdefault:
+      title: 'Gdefault'
+      description: 'When on, the ":substitute" flag \'g\' is default on'
+      type: 'boolean'
+      default: 'false'
diff --git a/lib/ex.coffee b/lib/ex.coffee
index a1e5ad3..cbc7857 100644
--- a/lib/ex.coffee
+++ b/lib/ex.coffee
@@ -18,7 +18,7 @@ trySave = (func) ->
 
   try
     response = func()
-    
+
     if response instanceof Promise
       response.then ->
         deferred.resolve()
@@ -361,6 +361,9 @@ class Ex
     try
       flagsObj = {}
       flags.split('').forEach((flag) -> flagsObj[flag] = true)
+      # gdefault option
+      if atom.config.get('ex-mode.gdefault')
+        flagsObj.g = !flagsObj.g
       patternRE = getSearchTerm(pattern, flagsObj)
     catch e
       if e.message.indexOf('Invalid flags supplied to RegExp constructor') is 0
diff --git a/lib/vim-option.coffee b/lib/vim-option.coffee
index ddf4688..223395f 100644
--- a/lib/vim-option.coffee
+++ b/lib/vim-option.coffee
@@ -56,4 +56,10 @@ class VimOption
   noscs: =>
     @nosmartcase()
 
+  gdefault: =>
+    atom.config.set("ex-mode.gdefault", true)
+
+  nogdefault: =>
+    atom.config.set("ex-mode.gdefault", false)
+
 module.exports = VimOption
diff --git a/spec/ex-commands-spec.coffee b/spec/ex-commands-spec.coffee
index 2eb252a..29f211e 100644
--- a/spec/ex-commands-spec.coffee
+++ b/spec/ex-commands-spec.coffee
@@ -715,6 +715,17 @@ describe "the commands", ->
       submitNormalModeInputText(':%substitute/abc/ghi/ig')
       expect(editor.getText()).toEqual('ghiaghi\ndefdDEF\nghiaghi')
 
+    it "set gdefault option", ->
+      openEx()
+      atom.config.set('ex-mode.gdefault', true)
+      submitNormalModeInputText(':substitute/a/x')
+      expect(editor.getText()).toEqual('xbcxABC\ndefdDEF\nabcaABC')
+
+      atom.commands.dispatch(editorElement, 'ex-mode:open')
+      atom.config.set('ex-mode.gdefault', true)
+      submitNormalModeInputText(':substitute/a/x/g')
+      expect(editor.getText()).toEqual('xbcaABC\ndefdDEF\nabcaABC')
+
     describe ":yank", ->
       beforeEach ->
         editor.setText('abc\ndef\nghi\njkl')
@@ -944,6 +955,14 @@ describe "the commands", ->
         submitNormalModeInputText(':set nosmartcase')
         expect(atom.config.get('vim-mode.useSmartcaseForSearch')).toBe(false)
 
+      it "sets (no)gdefault", ->
+        openEx()
+        submitNormalModeInputText(':set gdefault')
+        expect(atom.config.get('ex-mode.gdefault')).toBe(true)
+        atom.commands.dispatch(editorElement, 'ex-mode:open')
+        submitNormalModeInputText(':set nogdefault')
+        expect(atom.config.get('ex-mode.gdefault')).toBe(false)
+
   describe "aliases", ->
     it "calls the aliased function without arguments", ->
       ExClass.registerAlias('W', 'w')