diff --git a/app/models/optimized_image.rb b/app/models/optimized_image.rb
index 01f870baa6b..5e5e8e41919 100644
--- a/app/models/optimized_image.rb
+++ b/app/models/optimized_image.rb
@@ -318,9 +318,13 @@ class OptimizedImage < ActiveRecord::Base
     convert_with(instructions, to, opts)
   end
 
+  MAX_PNGQUANT_SIZE = 500_000
+
   def self.convert_with(instructions, to, opts = {})
     Discourse::Utils.execute_command(*instructions)
-    FileHelper.optimize_image!(to)
+
+    allow_pngquant = to.downcase.ends_with?(".png") && File.size(to) < MAX_PNGQUANT_SIZE
+    FileHelper.optimize_image!(to, allow_pngquant: allow_pngquant)
     true
   rescue => e
     if opts[:raise_on_error]
diff --git a/lib/file_helper.rb b/lib/file_helper.rb
index f146b8b139d..3f148fc278c 100644
--- a/lib/file_helper.rb
+++ b/lib/file_helper.rb
@@ -82,7 +82,12 @@ class FileHelper
     tmp
   end
 
-  def self.optimize_image!(filename)
+  def self.optimize_image!(filename, allow_pngquant: false)
+    pngquant_options = false
+    if allow_pngquant
+      pngquant_options = { allow_lossy: true }
+    end
+
     ImageOptim.new(
       # GLOBAL
       timeout: 15,
@@ -92,7 +97,7 @@ class FileHelper
       advpng: false,
       pngcrush: false,
       pngout: false,
-      pngquant: false,
+      pngquant: pngquant_options,
       # JPG
       jpegoptim: { strip: SiteSetting.strip_image_metadata ? "all" : "none" },
       jpegtran: false,
diff --git a/spec/fixtures/images/pngquant.png b/spec/fixtures/images/pngquant.png
new file mode 100644
index 00000000000..2ffb274f20a
Binary files /dev/null and b/spec/fixtures/images/pngquant.png differ
diff --git a/spec/lib/upload_creator_spec.rb b/spec/lib/upload_creator_spec.rb
index 04ac72f00b1..897c946aeea 100644
--- a/spec/lib/upload_creator_spec.rb
+++ b/spec/lib/upload_creator_spec.rb
@@ -98,6 +98,27 @@ RSpec.describe UploadCreator do
       end
     end
 
+    describe 'pngquant' do
+      let(:filename) { "pngquant.png" }
+      let(:file) { file_from_fixtures(filename) }
+
+      it 'should apply pngquant to optimized images' do
+        upload = UploadCreator.new(file, filename,
+          pasted: true,
+          force_optimize: true
+        ).create_for(user.id)
+
+        # no optimisation possible without losing details
+        expect(upload.filesize).to eq(9558)
+
+        thumbnail_size = upload.get_optimized_image(upload.width, upload.height, {}).filesize
+
+        # pngquant will lose some colors causing some extra size reduction
+        expect(thumbnail_size).to be < 7500
+      end
+
+    end
+
     describe 'converting to jpeg' do
       let(:filename) { "should_be_jpeg.png" }
       let(:file) { file_from_fixtures(filename) }
diff --git a/spec/models/optimized_image_spec.rb b/spec/models/optimized_image_spec.rb
index 45c96abbcd2..9aaa86442c8 100644
--- a/spec/models/optimized_image_spec.rb
+++ b/spec/models/optimized_image_spec.rb
@@ -6,7 +6,7 @@ describe OptimizedImage do
 
   unless ENV["TRAVIS"]
     describe '.crop' do
-      it 'should work correctly (requires correct version of image optim)' do
+      it 'should produce cropped images' do
         tmp_path = "/tmp/cropped.png"
 
         begin
@@ -17,12 +17,15 @@ describe OptimizedImage do
             5
           )
 
-          fixture_path = "#{Rails.root}/spec/fixtures/images/cropped.png"
-          fixture_hex = Digest::MD5.hexdigest(File.read(fixture_path))
+          # we don't want to deal with something new here every time image magick
+          # is upgraded or pngquant is upgraded, lets just test the basics ...
+          # cropped image should be less than 120 bytes
 
-          cropped_hex = Digest::MD5.hexdigest(File.read(tmp_path))
+          cropped_size = File.size(tmp_path)
+
+          expect(cropped_size).to be < 120
+          expect(cropped_size).to be > 50
 
-          expect(cropped_hex).to eq(fixture_hex)
         ensure
           File.delete(tmp_path) if File.exists?(tmp_path)
         end
@@ -128,7 +131,7 @@ describe OptimizedImage do
     end
 
     describe '.downsize' do
-      it 'should work correctly (requires correct version of image optim)' do
+      it 'should downsize logo' do
         tmp_path = "/tmp/downsized.png"
 
         begin
@@ -138,12 +141,10 @@ describe OptimizedImage do
             "100x100\>"
           )
 
-          fixture_path = "#{Rails.root}/spec/fixtures/images/downsized.png"
-          fixture_hex = Digest::MD5.hexdigest(File.read(fixture_path))
+          info = FastImage.new(tmp_path)
+          expect(info.size).to eq([100, 27])
+          expect(File.size(tmp_path)).to be < 2300
 
-          downsized_hex = Digest::MD5.hexdigest(File.read(tmp_path))
-
-          expect(downsized_hex).to eq(fixture_hex)
         ensure
           File.delete(tmp_path) if File.exists?(tmp_path)
         end