diff --git a/lib/compare.js b/lib/compare.js
index 35c8d51..bb1151c 100644
--- a/lib/compare.js
+++ b/lib/compare.js
@@ -21,9 +21,14 @@ module.exports = exports = function (proto) {
   function compare(orig, compareTo, options, cb) {
 
     var isImageMagick = this._options && this._options.imageMagick;
-    // compare binary for IM is `compare`, for GM it's `gm compare`
-    var bin = isImageMagick ? '' : 'gm ';
-    var args = ['compare', '-metric', 'mse', orig, compareTo]
+    var appPath = this._options && this._options.appPath || '';
+    var bin = isImageMagick
+      ? appPath + 'compare' 
+      : appPath + 'gm'
+    var args = ['-metric', 'mse', orig, compareTo]
+    if (!isImageMagick) {
+        args.unshift('compare');
+    }
     var tolerance = 0.4;
     // outputting the diff image
     if (typeof options === 'object') {
@@ -46,7 +51,7 @@ module.exports = exports = function (proto) {
             args.push(options.highlightStyle)
         }
         // For IM, filename is the last argument. For GM it's `-file <filename>`
-        if (isImageMagick) {
+        if (!isImageMagick) {
             args.push('-file');
         }
         args.push(options.file);
@@ -71,7 +76,7 @@ module.exports = exports = function (proto) {
       }
     }
 
-    var proc = spawn('/usr/bin/gm', args);
+    var proc = spawn(bin, args);
     var stdout = '';
     var stderr = '';
     proc.stdout.on('data',function(data) { stdout+=data });
diff --git a/test/422.js b/test/422.js
index 1f0d29e..583d969 100644
--- a/test/422.js
+++ b/test/422.js
@@ -29,11 +29,13 @@ module.exports = function (gm, dir, finish, GM) {
           if (err) return finish(err);
 
           fs.exists(options.file, function(exists) {
-            if (exists) finish();
+            if (exists) {
+		fs.unlink(options.file, finish);
+		}
             else finish(new Error('Diff file does not exist.'));
           });
         });
       });
     });
   });
-};
\ No newline at end of file
+};