diff --git a/docs/changelog.md b/docs/changelog.md
index e5da75dd..c805fecf 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -38,6 +38,10 @@ Requires libvips v8.3.1
   [#486](https://github.com/lovell/sharp/issues/486)
   [@kapouer](https://github.com/kapouer)
 
+* Allow images with an alpha channel to work with LAB-colourspace based sharpen.
+  [#490](https://github.com/lovell/sharp/issues/490)
+  [@jwagner](https://github.com/jwagner)
+
 #### v0.15.0 - 21<sup>st</sup> May 2016
 
 * Use libvips' new Lanczos 3 kernel as default for image reduction.
diff --git a/src/operations.cc b/src/operations.cc
index cdbc12cf..6adfe165 100644
--- a/src/operations.cc
+++ b/src/operations.cc
@@ -244,9 +244,13 @@ namespace sharp {
       return image.conv(sharpen);
     } else {
       // Slow, accurate sharpen in LAB colour space, with control over flat vs jagged areas
+      VipsInterpretation colourspaceBeforeSharpen = image.interpretation();
+      if (colourspaceBeforeSharpen == VIPS_INTERPRETATION_RGB) {
+        colourspaceBeforeSharpen = VIPS_INTERPRETATION_sRGB;
+      }
       return image.sharpen(
         VImage::option()->set("sigma", sigma)->set("m1", flat)->set("m2", jagged)
-      );
+      ).colourspace(colourspaceBeforeSharpen);
     }
   }
 
diff --git a/test/fixtures/expected/sharpen-rgba.png b/test/fixtures/expected/sharpen-rgba.png
new file mode 100644
index 00000000..841511ca
Binary files /dev/null and b/test/fixtures/expected/sharpen-rgba.png differ
diff --git a/test/unit/sharpen.js b/test/unit/sharpen.js
index 244059de..2b70a666 100644
--- a/test/unit/sharpen.js
+++ b/test/unit/sharpen.js
@@ -12,6 +12,7 @@ describe('Sharpen', function() {
       .resize(320, 240)
       .sharpen(6)
       .toBuffer(function(err, data, info) {
+        if (err) throw err;
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
         assert.strictEqual(240, info.height);
@@ -24,6 +25,7 @@ describe('Sharpen', function() {
       .resize(320, 240)
       .sharpen(1.5, 0.5, 2.5)
       .toBuffer(function(err, data, info) {
+        if (err) throw err;
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
         assert.strictEqual(240, info.height);
@@ -36,6 +38,7 @@ describe('Sharpen', function() {
       .resize(320, 240)
       .sharpen(3.5, 2, 4)
       .toBuffer(function(err, data, info) {
+        if (err) throw err;
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
         assert.strictEqual(240, info.height);
@@ -43,11 +46,26 @@ describe('Sharpen', function() {
       });
   });
 
+  it('specific radius/levels with alpha channel', function(done) {
+    sharp(fixtures.inputPngWithTransparency)
+      .resize(320, 240)
+      .sharpen(5, 4, 8)
+      .toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual('png', info.format);
+        assert.strictEqual(4, info.channels);
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fixtures.assertSimilar(fixtures.expected('sharpen-rgba.png'), data, done);
+      });
+  });
+
   it('mild sharpen', function(done) {
     sharp(fixtures.inputJpg)
       .resize(320, 240)
       .sharpen()
       .toBuffer(function(err, data, info) {
+        if (err) throw err;
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
         assert.strictEqual(240, info.height);
@@ -78,6 +96,7 @@ describe('Sharpen', function() {
       .resize(320, 240)
       .sharpen(false)
       .toBuffer(function(err, notSharpened, info) {
+        if (err) throw err;
         assert.strictEqual(true, notSharpened.length > 0);
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
@@ -86,6 +105,7 @@ describe('Sharpen', function() {
           .resize(320, 240)
           .sharpen(true)
           .toBuffer(function(err, sharpened, info) {
+            if (err) throw err;
             assert.strictEqual(true, sharpened.length > 0);
             assert.strictEqual(true, sharpened.length > notSharpened.length);
             assert.strictEqual('jpeg', info.format);