diff --git a/package.json b/package.json
index ad0ec609..214479c9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "sharp",
-  "version": "0.11.0",
+  "version": "0.11.1",
   "author": "Lovell Fuller <npm@lovell.info>",
   "contributors": [
     "Pierre Inglebert <pierre.inglebert@gmail.com>",
@@ -51,7 +51,7 @@
     "semver": "^5.0.1"
   },
   "devDependencies": {
-    "async": "^1.3.0",
+    "async": "^1.4.2",
     "coveralls": "^2.11.2",
     "exif-reader": "1.0.0",
     "icc": "^0.0.2",
diff --git a/src/pipeline.cc b/src/pipeline.cc
index e0e2ce08..05567249 100755
--- a/src/pipeline.cc
+++ b/src/pipeline.cc
@@ -445,7 +445,7 @@ class PipelineWorker : public NanAsyncWorker {
     }
 
     // Gamma encoding (darken)
-    if (baton->gamma >= 1 && baton->gamma <= 3) {
+    if (baton->gamma >= 1 && baton->gamma <= 3 && !HasAlpha(image)) {
       VipsImage *gammaEncoded;
       if (vips_gamma(image, &gammaEncoded, "exponent", 1.0 / baton->gamma, NULL)) {
         return Error();
@@ -493,11 +493,9 @@ class PipelineWorker : public NanAsyncWorker {
     }
 
     bool shouldAffineTransform = xresidual != 0.0 || yresidual != 0.0;
-    bool shouldBlur = baton->blurSigma != 0.0;
-    bool shouldSharpen = baton->sharpenRadius != 0;
-    bool shouldTransform = shouldAffineTransform || shouldBlur || shouldSharpen;
+    bool willConvolve = baton->blurSigma > 0.0 || baton->sharpenRadius > 0;
     bool hasOverlay = !baton->overlayPath.empty();
-    bool shouldPremultiplyAlpha = HasAlpha(image) && image->Bands == 4 && (shouldTransform || hasOverlay);
+    bool shouldPremultiplyAlpha = HasAlpha(image) && (shouldAffineTransform || willConvolve || hasOverlay);
 
     // Premultiply image alpha channel before all transformations to avoid
     // dark fringing around bright pixels
@@ -681,7 +679,7 @@ class PipelineWorker : public NanAsyncWorker {
     }
 
     // Blur
-    if (shouldBlur) {
+    if (baton->blurSigma != 0.0) {
       VipsImage *blurred;
       if (Blur(hook, image, &blurred, baton->blurSigma)) {
         return Error();
@@ -690,7 +688,7 @@ class PipelineWorker : public NanAsyncWorker {
     }
 
     // Sharpen
-    if (shouldSharpen) {
+    if (baton->sharpenRadius != 0) {
       VipsImage *sharpened;
       if (Sharpen(hook, image, &sharpened, baton->sharpenRadius, baton->sharpenFlat, baton->sharpenJagged)) {
         return Error();
@@ -698,25 +696,6 @@ class PipelineWorker : public NanAsyncWorker {
       image = sharpened;
     }
 
-    // Gamma decoding (brighten)
-    if (baton->gamma >= 1 && baton->gamma <= 3) {
-      VipsImage *gammaDecoded;
-      if (vips_gamma(image, &gammaDecoded, "exponent", baton->gamma, NULL)) {
-        return Error();
-      }
-      vips_object_local(hook, gammaDecoded);
-      image = gammaDecoded;
-    }
-
-    // Apply normalization - stretch luminance to cover full dynamic range
-    if (baton->normalize) {
-      VipsImage *normalized;
-      if (Normalize(hook, image, &normalized)) {
-        return Error();
-      }
-      image = normalized;
-    }
-
     // Composite with overlay, if present
     if (hasOverlay) {
       VipsImage *overlayImage = NULL;
@@ -789,6 +768,25 @@ class PipelineWorker : public NanAsyncWorker {
       image = imageUnpremultiplied;
     }
 
+    // Gamma decoding (brighten)
+    if (baton->gamma >= 1 && baton->gamma <= 3 && !HasAlpha(image)) {
+      VipsImage *gammaDecoded;
+      if (vips_gamma(image, &gammaDecoded, "exponent", baton->gamma, NULL)) {
+        return Error();
+      }
+      vips_object_local(hook, gammaDecoded);
+      image = gammaDecoded;
+    }
+
+    // Apply normalization - stretch luminance to cover full dynamic range
+    if (baton->normalize) {
+      VipsImage *normalized;
+      if (Normalize(hook, image, &normalized)) {
+        return Error();
+      }
+      image = normalized;
+    }
+
     // Convert image to sRGB, if not already
     if (image->Type != VIPS_INTERPRETATION_sRGB) {
       // Switch interpretation to sRGB
diff --git a/test/fixtures/expected/gamma-0.0.jpg b/test/fixtures/expected/gamma-0.0.jpg
new file mode 100644
index 00000000..59daf1ac
Binary files /dev/null and b/test/fixtures/expected/gamma-0.0.jpg differ
diff --git a/test/fixtures/expected/gamma-2.2.jpg b/test/fixtures/expected/gamma-2.2.jpg
new file mode 100644
index 00000000..1e876f98
Binary files /dev/null and b/test/fixtures/expected/gamma-2.2.jpg differ
diff --git a/test/fixtures/expected/gamma-3.0.jpg b/test/fixtures/expected/gamma-3.0.jpg
new file mode 100644
index 00000000..88048ba2
Binary files /dev/null and b/test/fixtures/expected/gamma-3.0.jpg differ
diff --git a/test/fixtures/expected/gamma-alpha.jpg b/test/fixtures/expected/gamma-alpha.jpg
new file mode 100644
index 00000000..08b54565
Binary files /dev/null and b/test/fixtures/expected/gamma-alpha.jpg differ
diff --git a/test/unit/gamma.js b/test/unit/gamma.js
index 350a9ef9..b109e28e 100755
--- a/test/unit/gamma.js
+++ b/test/unit/gamma.js
@@ -12,32 +12,53 @@ describe('Gamma correction', function() {
   it('value of 0.0 (disabled)', function(done) {
     sharp(fixtures.inputJpgWithGammaHoliness)
       .resize(129, 111)
-      .toFile(fixtures.path('output.gamma-0.0.jpg'), done);
+      .toBuffer(function(err, data, info) {
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(129, info.width);
+        assert.strictEqual(111, info.height);
+        fixtures.assertSimilar(fixtures.expected('gamma-0.0.jpg'), data, done);
+      });
   });
 
   it('value of 2.2 (default)', function(done) {
     sharp(fixtures.inputJpgWithGammaHoliness)
       .resize(129, 111)
       .gamma()
-      .toFile(fixtures.path('output.gamma-2.2.jpg'), done);
+      .toBuffer(function(err, data, info) {
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(129, info.width);
+        assert.strictEqual(111, info.height);
+        fixtures.assertSimilar(fixtures.expected('gamma-2.2.jpg'), data, done);
+      });
   });
 
   it('value of 3.0', function(done) {
     sharp(fixtures.inputJpgWithGammaHoliness)
       .resize(129, 111)
       .gamma(3)
-      .toFile(fixtures.path('output.gamma-3.0.jpg'), done);
+      .toBuffer(function(err, data, info) {
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(129, info.width);
+        assert.strictEqual(111, info.height);
+        fixtures.assertSimilar(fixtures.expected('gamma-3.0.jpg'), data, done);
+      });
   });
 
-  it('invalid value', function(done) {
-    var isValid = true;
-    try {
+  it('alpha transparency', function(done) {
+    sharp(fixtures.inputPngOverlayLayer1)
+      .resize(320)
+      .gamma()
+      .toBuffer(function(err, data, info) {
+        assert.strictEqual('png', info.format);
+        assert.strictEqual(320, info.width);
+        fixtures.assertSimilar(fixtures.expected('gamma-alpha.jpg'), data, done);
+      });
+  });
+
+  it('invalid value', function() {
+    assert.throws(function() {
       sharp(fixtures.inputJpgWithGammaHoliness).gamma(4);
-    } catch (err) {
-      isValid = false;
-    }
-    assert.strictEqual(false, isValid);
-    done();
+    });
   });
 
 });