diff --git a/CHANGELOG.md b/CHANGELOG.md
index e4bb5623..52f0dd2c 100755
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,9 @@ postcssImport({
 })
 ```
 
+- Changed: support promise in `transform` option and `undefined` result will be skipped
+([#147](https://github.com/postcss/postcss-import/pull/147))
+
 # 7.1.3 - 2015-11-05
 
 - Fixed: ensure node 0.12 compatibility, round 2
diff --git a/README.md b/README.md
index 4063eca2..8f5824bc 100755
--- a/README.md
+++ b/README.md
@@ -109,7 +109,8 @@ _Note: nested `@import` will additionally benefit of the relative dirname of imp
 Type: `Function`  
 Default: `null`
 
-A function to transform the content of imported files. Take one argument (file content) & should return the modified content.
+A function to transform the content of imported files. Take one argument (file content) and should return the modified content or promise with it.
+`undefined` result will be skipped.
 
 #### `plugins`
 
diff --git a/index.js b/index.js
index d77495bf..72d32615 100755
--- a/index.js
+++ b/index.js
@@ -284,10 +284,15 @@ function loadImportContent(
 
   return Promise.resolve(options.load(filename, options))
   .then(function(content) {
-    if (typeof options.transform === "function") {
-      content = options.transform(content, filename)
+    if (typeof options.transform !== "function") {
+      return content
     }
-
+    return Promise.resolve(options.transform(content, filename, options))
+    .then(function(transformed) {
+      return typeof transformed === "string" ? transformed : content
+    })
+  })
+  .then(function(content) {
     if (content.trim() === "") {
       result.warn(filename + " is empty", { node: atRule })
       return
diff --git a/package.json b/package.json
index 4ae27683..cade715a 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,6 @@
   },
   "devDependencies": {
     "ava": "^0.8.0",
-    "css-whitespace": "^1.1.1",
     "eslint": "^1.1.0",
     "postcss-scss": "^0.1.3"
   },
diff --git a/test/fixtures/imports/foo.styl b/test/fixtures/imports/foo.styl
deleted file mode 100755
index 59bb3b52..00000000
--- a/test/fixtures/imports/foo.styl
+++ /dev/null
@@ -1,2 +0,0 @@
-foo
-  styl: true
diff --git a/test/fixtures/transform-content.css b/test/fixtures/transform-content.css
new file mode 100644
index 00000000..0a2e522a
--- /dev/null
+++ b/test/fixtures/transform-content.css
@@ -0,0 +1 @@
+@import "foo"
diff --git a/test/fixtures/transform-content.expected.css b/test/fixtures/transform-content.expected.css
new file mode 100644
index 00000000..44fe46f6
--- /dev/null
+++ b/test/fixtures/transform-content.expected.css
@@ -0,0 +1 @@
+transformed-content {}
diff --git a/test/fixtures/transform-undefined.css b/test/fixtures/transform-undefined.css
new file mode 100644
index 00000000..0a2e522a
--- /dev/null
+++ b/test/fixtures/transform-undefined.css
@@ -0,0 +1 @@
+@import "foo"
diff --git a/test/fixtures/transform-undefined.expected.css b/test/fixtures/transform-undefined.expected.css
new file mode 100644
index 00000000..d2d19a3e
--- /dev/null
+++ b/test/fixtures/transform-undefined.expected.css
@@ -0,0 +1 @@
+foo{}
diff --git a/test/fixtures/transform.css b/test/fixtures/transform.css
deleted file mode 100755
index 6ac154ab..00000000
--- a/test/fixtures/transform.css
+++ /dev/null
@@ -1,4 +0,0 @@
-@import "foo.styl";
-@import "foo.styl" (min-width: 25em);
-
-content{}
diff --git a/test/fixtures/transform.expected.css b/test/fixtures/transform.expected.css
deleted file mode 100755
index 7ac882c4..00000000
--- a/test/fixtures/transform.expected.css
+++ /dev/null
@@ -1,9 +0,0 @@
-foo {
-  styl: true;
-}
-@media (min-width: 25em) {
-foo {
-  styl: true;
-}
-}
-content{}
diff --git a/test/import.js b/test/import.js
index 57cc4663..c4bfe0d9 100644
--- a/test/import.js
+++ b/test/import.js
@@ -31,12 +31,6 @@ test("should import stylsheets relatively", t => {
   return compareFixtures(t, "relative")
 })
 
-test("should support transform", t => {
-  return compareFixtures(t, "transform", {
-    transform: require("css-whitespace"),
-  })
-})
-
 test("should work without a specified path", t => {
   return compareFixtures(t, "cwd")
 })
diff --git a/test/transform.js b/test/transform.js
new file mode 100644
index 00000000..988b303f
--- /dev/null
+++ b/test/transform.js
@@ -0,0 +1,26 @@
+import test from "ava"
+import compareFixtures from "./lib/compare-fixtures"
+
+test.serial("should accept content", t => {
+  return compareFixtures(t, "transform-content", {
+    transform: () => "transformed-content {}",
+  })
+})
+
+test.serial("should accept promised content", t => {
+  return compareFixtures(t, "transform-content", {
+    transform: () => Promise.resolve("transformed-content {}"),
+  })
+})
+
+test.serial("should ignore returned undefined", t => {
+  return compareFixtures(t, "transform-undefined", {
+    transform: () => undefined,
+  })
+})
+
+test.serial("should ignore promised undefined", t => {
+  return compareFixtures(t, "transform-undefined", {
+    transform: () => Promise.resolve(undefined),
+  })
+})