Adds check to make sure duplicates are not created.

index.js

@@ -6,6 +6,15 @@ module.exports = postcss.plugin('postcss-initial', function (opts) {
   opts.reset = opts.reset || 'all';
   opts.replace = opts.replace || false;
   var getFallback = makeFallbackFunction(opts.reset === 'inherited');
+  var getPropPrevTo = function (prop, decl) {
+    var foundPrev = false;
+    decl.parent.walkDecls(function (child) {
+      if (child.prop === decl.prop && child.value !== decl.value) {
+        foundPrev = true;
+      }
+    });
+    return foundPrev;
+  };
   return function (css) {
     css.walkDecls(function (decl) {
       if (decl.value.indexOf('initial') < 0) {
@@ -14,7 +23,9 @@ module.exports = postcss.plugin('postcss-initial', function (opts) {
       var fallBackRules = getFallback(decl.prop, decl.value);
       if (fallBackRules.length === 0) return;
       fallBackRules.forEach(function (rule) {
-        decl.cloneBefore(rule);
+        if ( !getPropPrevTo(decl.prop, decl) ) {
+          decl.cloneBefore(rule);
+        }
       });
       if (opts.replace === true) {
         decl.remove();

test/fixtures/no-duplication.css

@@ -0,0 +1,6 @@
+a {
+  overflow: visible;
+  overflow: initial;
+  width: auto;
+  width: initial;
+}

test/fixtures/no-duplication.expected.css

@@ -0,0 +1,6 @@
+a {
+  overflow: visible;
+  overflow: initial;
+  width: auto;
+  width: initial;
+}

test/index.js

@@ -34,6 +34,12 @@ describe('postcss-initial', function () {
       f('unknown.expected')
     );
   });
+  it('no duplication', function () {
+    test(
+      f('no-duplication'),
+      f('no-duplication.expected')
+    );
+  });
   it('all:initial - default styles', function () {
     test(
       f('all-initial-default'),