diff --git a/framework/console/controllers/AssetController.php b/framework/console/controllers/AssetController.php
index 28c568b708..9392c33bd7 100644
--- a/framework/console/controllers/AssetController.php
+++ b/framework/console/controllers/AssetController.php
@@ -512,9 +512,10 @@ EOD;
     public function combineCssFiles($inputFiles, $outputFile)
     {
         $content = '';
+        $outputFilePath = dirname($this->findRealPath($outputFile));
         foreach ($inputFiles as $file) {
             $content .= "/*** BEGIN FILE: $file ***/\n"
-                . $this->adjustCssUrl(file_get_contents($file), dirname($file), dirname($outputFile))
+                . $this->adjustCssUrl(file_get_contents($file), dirname($this->findRealPath($file)), $outputFilePath)
                 . "/*** END FILE: $file ***/\n";
         }
         if (!file_put_contents($outputFile, $content)) {
@@ -658,4 +659,26 @@ EOD;
             echo "Configuration file template created at '{$configFile}'.\n\n";
         }
     }
+
+    /**
+     * Returns canonicalized absolute pathname.
+     * Unlike regular `realpath()` this method does not expand symlinks and does not check path existence.
+     * @param string $path raw path
+     * @return string canonicalized absolute pathname
+     */
+    private function findRealPath($path)
+    {
+        $path = str_replace(['/', '\\'], DIRECTORY_SEPARATOR, $path);
+        $pathParts = explode(DIRECTORY_SEPARATOR, $path);
+
+        $realPathParts = [];
+        foreach ($pathParts as $pathPart) {
+            if ($pathPart === '..') {
+                array_pop($realPathParts);
+            } else {
+                array_push($realPathParts, $pathPart);
+            }
+        }
+        return implode(DIRECTORY_SEPARATOR, $realPathParts);
+    }
 }
diff --git a/tests/unit/framework/console/controllers/AssetControllerTest.php b/tests/unit/framework/console/controllers/AssetControllerTest.php
index 0b1ae94e66..534e7f07cd 100644
--- a/tests/unit/framework/console/controllers/AssetControllerTest.php
+++ b/tests/unit/framework/console/controllers/AssetControllerTest.php
@@ -409,4 +409,51 @@ EOL;
 
         $this->assertEquals($expectedCssContent, $adjustedCssContent, 'Unable to adjust CSS correctly!');
     }
+
+    /**
+     * Data provider for [[testFindRealPath()]]
+     * @return array test data
+     */
+    public function findRealPathDataProvider()
+    {
+        return [
+            [
+                '/linux/absolute/path',
+                '/linux/absolute/path',
+            ],
+            [
+                '/linux/up/../path',
+                '/linux/path',
+            ],
+            [
+                '/linux/twice/up/../../path',
+                '/linux/path',
+            ],
+            [
+                '/linux/../mix/up/../path',
+                '/mix/path',
+            ],
+            [
+                'C:\\windows\\absolute\\path',
+                'C:\\windows\\absolute\\path',
+            ],
+            [
+                'C:\\windows\\up\\..\\path',
+                'C:\\windows\\path',
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider findRealPathDataProvider
+     *
+     * @param string $sourcePath
+     * @param string $expectedRealPath
+     */
+    public function testFindRealPath($sourcePath, $expectedRealPath)
+    {
+        $expectedRealPath = str_replace(['/', '\\'], DIRECTORY_SEPARATOR, $expectedRealPath);
+        $realPath = $this->invokeAssetControllerMethod('findRealPath', [$sourcePath]);
+        $this->assertEquals($expectedRealPath, $realPath);
+    }
 }