diff --git a/index.js b/index.js
index 81f500f..bb0a830 100644
--- a/index.js
+++ b/index.js
@@ -11,6 +11,7 @@ var Vinyl           = require('vinyl');
 var fancyLog        = require('fancy-log');
 var merge           = require('merge');
 var applySourcemap  = require('vinyl-sourcemaps-apply');
+var crypto          = require('crypto');
 
 var Concat          = require('concat-with-sourcemaps');
 
@@ -111,7 +112,12 @@ module.exports = function(options){
             };
 
             var addImports = function(aFile, fileNamesOfPartsToImport){
-                var parameters = options.cacheBuster ? '?z=' + Math.round((Math.random() * 999)) : '';
+                var generated_hash = crypto
+                    .createHash('sha1')
+                    .update(aFile.contents, 'binary')
+                    .digest('hex');
+
+                var parameters = options.cacheBuster ? '?z=' + generated_hash : '';
                 var filePath = path.relative(aFile.base, aFile.path);
                 var concat = new Concat(shouldCreateSourcemaps, filePath, '\n');
                 for (var i = 0; i < fileNamesOfPartsToImport.length; i++) {
diff --git a/test/main.js b/test/main.js
index 11e67a7..2e7f21f 100644
--- a/test/main.js
+++ b/test/main.js
@@ -123,7 +123,7 @@ describe('gulp-bless', function() {
                             var expectedSplitFile = expectedSplits[index];
                             newFile.relative.should.equal(path.basename(expectedSplitFile.path));
 
-                            var contents = newFile.contents.toString('utf8').replace(/\?z=[0-9]+'\)/g, "?z=xxx')");
+                            var contents = newFile.contents.toString('utf8').replace(/\?z=[0-9a-f]+'\)/g, "?z=xxx')");
 
                             contents.should.equal(expectedSplitFile.contents.toString('utf8'));
                             Buffer.isBuffer(newFile.contents).should.equal(true);
@@ -181,7 +181,7 @@ describe('gulp-bless', function() {
                     should.exist(masterPart);
                     should.exist(subPart);
                     path.basename(subPart.path).should.equal("long-split" + suffix + "1.css");
-                    var importRegex = "@import url\\('long-split" + suffix  + "1.css\\?z=[0-9]+'\\);";
+                    var importRegex = "@import url\\('long-split" + suffix  + "1.css\\?z=[0-9a-f]+'\\);";
                     masterPart.contents.toString("utf8").should.match(new RegExp(importRegex));
                     done();
                 });
@@ -231,7 +231,7 @@ describe('gulp-bless', function() {
                     should.exist(masterPart);
                     should.exist(subPart);
                     path.basename(subPart.path).should.equal("long-split" + suffix + "-1.css");
-                    var importRegex = "@import url\\('long-split" + suffix  + "-1.css\\?z=[0-9]+'\\);";
+                    var importRegex = "@import url\\('long-split" + suffix  + "-1.css\\?z=[0-9a-f]+'\\);";
                     masterPart.contents.toString("utf8").should.match(new RegExp(importRegex));
                     done();
                 });
@@ -276,7 +276,7 @@ describe('gulp-bless', function() {
                 .pipe(assert.first(function(result) {
                     path.relative('./', result.path).should.equal(path.relative('/home', expectedSplits[0].path));
                     result.contents.toString('utf8')
-                        .replace(/\?z=[0-9]+'\)/g, "?z=xxx')")
+                        .replace(/\?z=[0-9a-f]+'\)/g, "?z=xxx')")
                         .should.equal(expectedSplits[0].contents.toString('utf8'));
 
                     result.sourceMap.sources.should.have.length(1);
@@ -399,7 +399,7 @@ describe('gulp-bless', function() {
                 .pipe(assert.nth(1, function(result) {
                     path.relative('./', result.path).should.equal(path.relative('/home', expectedSplits[0].path));
                     result.contents.toString('utf8')
-                        .replace(/\?z=[0-9]+\)/g, "?z=xxx)")
+                        .replace(/\?z=[0-9a-f]+\)/g, "?z=xxx)")
                         .should.equal(expectedSplits[0].contents.toString('utf8'), "not equal to content of file ./test/css/long-split-with-sourcemap-comment.css");
 
                     result.sourceMap.sources.should.have.length(1);
@@ -564,7 +564,7 @@ describe('gulp-bless', function() {
                             var expectedSplitFile = expectedSplits[index];
                             newFile.relative.should.equal(path.basename(expectedSplitFile.path));
 
-                            var contents = newFile.contents.toString('utf8').replace(/\?z=[0-9]+'\)/g, "?z=xxx')");
+                            var contents = newFile.contents.toString('utf8').replace(/\?z=[0-9a-f]+'\)/g, "?z=xxx')");
 
                             contents.should.equal(expectedSplitFile.contents.toString('utf8'));
                             Buffer.isBuffer(newFile.contents).should.equal(true);