diff --git a/app/helpers/diff_helper.rb b/app/helpers/diff_helper.rb
index 93f12198a58..fd7b71407f3 100644
--- a/app/helpers/diff_helper.rb
+++ b/app/helpers/diff_helper.rb
@@ -8,6 +8,10 @@ module DiffHelper
     [marked_old_line, marked_new_line]
   end
 
+  def expand_all?
+    @expand_all || params[:expand].present?
+  end
+
   def render_diff_for_path(diffs, diff_refs, project)
     diff_file = safe_diff_files(diffs, diff_refs).first
 
diff --git a/app/views/projects/diffs/_content.html.haml b/app/views/projects/diffs/_content.html.haml
index 9c6a17c0a8c..5f4572ab9b0 100644
--- a/app/views/projects/diffs/_content.html.haml
+++ b/app/views/projects/diffs/_content.html.haml
@@ -9,7 +9,7 @@
     - if !project.repository.diffable?(blob)
       .nothing-here-block This diff was suppressed by a .gitattributes entry.
     - elsif diff_file.diff_lines.length > 0
-      - if diff_file.collapsed_by_default? && !@expand_all
+      - if diff_file.collapsed_by_default? && !expand_all?
         - url = url_for(params.merge(action: :diff_for_path, path: diff_file.file_path, format: nil))
         .nothing-here-block.diff-collapsed{data: { diff_for_path: url } }
           This diff is collapsed. Click to expand it.
diff --git a/app/views/projects/diffs/_diffs.html.haml b/app/views/projects/diffs/_diffs.html.haml
index 1975287faee..7b530af0f4a 100644
--- a/app/views/projects/diffs/_diffs.html.haml
+++ b/app/views/projects/diffs/_diffs.html.haml
@@ -6,6 +6,8 @@
 
 .content-block.oneline-block.files-changed
   .inline-parallel-buttons
+    - unless expand_all?
+      = link_to 'Expand all', url_for(params.merge(expand: 1, format: 'html')), class: 'btn btn-default'
     - if show_whitespace_toggle
       - if current_controller?(:commit)
         = commit_diff_whitespace_link(@project, @commit, class: 'hidden-xs')
diff --git a/spec/features/merge_requests/expand_collapse_diffs_spec.rb b/spec/features/merge_requests/expand_collapse_diffs_spec.rb
index 173ea3720da..f9c89c4ad96 100644
--- a/spec/features/merge_requests/expand_collapse_diffs_spec.rb
+++ b/spec/features/merge_requests/expand_collapse_diffs_spec.rb
@@ -135,4 +135,42 @@ feature 'Expand and collapse diffs', js: true, feature: true do
       end
     end
   end
+
+  context 'expanding all diffs' do
+    before do
+      click_link('Expand all')
+      wait_for_ajax
+      execute_script('window.ajaxUris = []; $(document).ajaxSend(function(event, xhr, settings) { ajaxUris.push(settings.url) });')
+    end
+
+    it 'reloads the page with all diffs expanded' do
+      expect(small_diff).to have_selector('.code')
+      expect(small_diff).not_to have_selector('.nothing-here-block')
+
+      expect(large_diff).to have_selector('.code')
+      expect(large_diff).not_to have_selector('.nothing-here-block')
+    end
+
+    context 'collapsing an expanded diff' do
+      before { click_link('small_diff.md') }
+
+      it 'hides the diff content' do
+        expect(small_diff).not_to have_selector('.code')
+        expect(small_diff).to have_selector('.nothing-here-block')
+      end
+
+      context 're-expanding the same diff' do
+        before { click_link('small_diff.md') }
+
+        it 'shows the diff content' do
+          expect(small_diff).to have_selector('.code')
+          expect(small_diff).not_to have_selector('.nothing-here-block')
+        end
+
+        it 'does not make a new HTTP request' do
+          expect(evaluate_script('ajaxUris')).to be_empty
+        end
+      end
+    end
+  end
 end