diff --git a/lib/getFilterInfosAndTargetContentTypeFromQueryString.js b/lib/getFilterInfosAndTargetContentTypeFromQueryString.js
index 54a4983..08020f1 100644
--- a/lib/getFilterInfosAndTargetContentTypeFromQueryString.js
+++ b/lib/getFilterInfosAndTargetContentTypeFromQueryString.js
@@ -182,7 +182,15 @@ module.exports = function getFilterInfosAndTargetContentTypeFromQueryString(quer
         currentEngineName = undefined;
     }
 
-    queryString.split('&').forEach(function (keyValuePair) {
+    var keyValuePairs = queryString.split('&');
+
+    if (sourceMetadata.contentType === 'image/gif' && !keyValuePairs.some(function (keyValuePair) {
+        return keyValuePair === 'png' || keyValuePair === 'webp' || keyValuePair === 'jpeg';
+    })) {
+        currentEngineName = 'gm';
+    }
+
+    keyValuePairs.forEach(function (keyValuePair) {
         var matchKeyValuePair = keyValuePair.match(/^([^=]+)(?:=(.*))?/);
         if (matchKeyValuePair) {
             var operationName = decodeURIComponent(matchKeyValuePair[1]),
diff --git a/lib/processImage.js b/lib/processImage.js
index 1624f26..98b2e27 100644
--- a/lib/processImage.js
+++ b/lib/processImage.js
@@ -94,6 +94,10 @@ module.exports = function (options) {
                     if (targetContentType) {
                         res.setHeader('Content-Type', targetContentType);
                     }
+                    if (options.debug) {
+                        // Only used by the test suite to assert that the right engine is used to process gifs:
+                        res.setHeader('X-Express-Processimage', filterInfosAndTargetFormat.operationNames.join(','));
+                    }
                     res.removeHeader('Content-Length');
                     var oldETag = res.getHeader('ETag'),
                         newETag;
diff --git a/test/processImage.js b/test/processImage.js
index 64ae322..74430bf 100644
--- a/test/processImage.js
+++ b/test/processImage.js
@@ -417,5 +417,62 @@ describe('express-processimage', function () {
                 errorPassedToNext: /bad extract area/
             });
         });
+
+        it('should convert an animated gif to png', function () {
+            return expect('GET /animated.gif?png', 'to yield response', {
+                body: expect.it('to have metadata satisfying', {
+                    format: 'PNG',
+                    size: {
+                        width: 23,
+                        height: 20
+                    }
+                })
+            });
+        });
+
+        it('should resize an animated gif using gm', function () {
+            config.debug = true;
+            return expect('GET /animated.gif?resize=40', 'to yield response', {
+                headers: {
+                    'X-Express-Processimage': 'gm'
+                },
+                body: expect.it('to have metadata satisfying', {
+                    format: 'GIF',
+                    size: {
+                        width: 40
+                    }
+                })
+            });
+        });
+
+        it('should resize a non-animated gif using gm', function () {
+            config.debug = true;
+            return expect('GET /bulb.gif?resize=200,200', 'to yield response', {
+                headers: {
+                    'X-Express-Processimage': 'gm'
+                },
+                body: expect.it('to have metadata satisfying', {
+                    format: 'GIF',
+                    size: {
+                        width: 200
+                    }
+                })
+            });
+        });
+
+        it('should use sharp when a gif is converted to png', function () {
+            config.debug = true;
+            return expect('GET /animated.gif?resize=40&png', 'to yield response', {
+                headers: {
+                    'X-Express-Processimage': 'sharp'
+                },
+                body: expect.it('to have metadata satisfying', {
+                    format: 'PNG',
+                    size: {
+                        width: 40
+                    }
+                })
+            });
+        });
     });
 });
diff --git a/testdata/animated.gif b/testdata/animated.gif
new file mode 100644
index 0000000..0358db2
Binary files /dev/null and b/testdata/animated.gif differ
diff --git a/testdata/bulb.gif b/testdata/bulb.gif
new file mode 100644
index 0000000..283c23e
Binary files /dev/null and b/testdata/bulb.gif differ