diff --git a/spec/language-mode-spec.coffee b/spec/language-mode-spec.coffee
index 35f143636..51cb7c36c 100644
--- a/spec/language-mode-spec.coffee
+++ b/spec/language-mode-spec.coffee
@@ -208,6 +208,20 @@ describe "LanguageMode", ->
         languageMode.toggleLineCommentsForBufferRows(0, 0)
         expect(buffer.lineForRow(0)).toBe "// @color: #4D926F;"
 
+  describe "xml", ->
+    beforeEach ->
+      editor = atom.project.openSync('sample.xml', autoIndent: false)
+      editor.setText("<!-- test -->")
+      {buffer, languageMode} = editor
+
+      waitsForPromise ->
+        atom.packages.activatePackage('language-xml')
+
+    describe "when uncommenting lines", ->
+      it "removes the leading whitespace from the comment end pattern match", ->
+        languageMode.toggleLineCommentsForBufferRows(0, 0)
+        expect(buffer.lineForRow(0)).toBe "test"
+
   describe "folding", ->
     beforeEach ->
       editor = atom.project.openSync('sample.js', autoIndent: false)
diff --git a/src/language-mode.coffee b/src/language-mode.coffee
index 0d7880cfe..093995947 100644
--- a/src/language-mode.coffee
+++ b/src/language-mode.coffee
@@ -39,13 +39,13 @@ class LanguageMode
     return unless commentStartString
 
     buffer = @editor.buffer
-    commentStartRegexString = _.escapeRegExp(commentStartString).replace(/(\s+)$/, '($1)?')
+    commentStartRegexString = _.escapeRegExp(commentStartString).replace(/(\s+)$/, '(?:$1)?')
     commentStartRegex = new OnigRegExp("^(\\s*)(#{commentStartRegexString})")
     shouldUncomment = commentStartRegex.test(buffer.lineForRow(start))
 
     if commentEndString
       if shouldUncomment
-        commentEndRegexString = _.escapeRegExp(commentEndString).replace(/^(\s+)/, '($1)?')
+        commentEndRegexString = _.escapeRegExp(commentEndString).replace(/^(\s+)/, '(?:$1)?')
         commentEndRegex = new OnigRegExp("(#{commentEndRegexString})(\\s*)$")
         startMatch =  commentStartRegex.search(buffer.lineForRow(start))
         endMatch = commentEndRegex.search(buffer.lineForRow(end))