diff --git a/src/View/Requirements_Backend.php b/src/View/Requirements_Backend.php
index aa6015ecd..d0bde0851 100644
--- a/src/View/Requirements_Backend.php
+++ b/src/View/Requirements_Backend.php
@@ -19,6 +19,7 @@ use SilverStripe\Dev\Debug;
 use SilverStripe\Dev\Deprecation;
 use SilverStripe\i18n\i18n;
 use SilverStripe\ORM\FieldType\DBField;
+use Symfony\Component\Filesystem\Path as FilesystemPath;
 
 class Requirements_Backend
 {
@@ -1454,19 +1455,12 @@ MESSAGE
         }
         $fileUrl = Injector::inst()->get(ResourceURLGenerator::class)->urlForResource($filePath);
         $fileUrlDir = dirname($fileUrl);
-        $content = preg_replace_callback('#([\s\'"\(])((:?[\.]{1,2}/)+)#', function ($a) use ($fileUrlDir) {
-            [ $_, $prefix, $match ] = $a;
-            $full = $fileUrlDir . '/' . $match;
-            $full = preg_replace('#/{2,}#', '/', $full); // ensure there's no repeated slashes
-            while (strpos($full, './') > 0) {
-                $post = $full;
-                $post = preg_replace('#([^/\.]+)/\.\./#', '', $post); // erase 'something/../' with the predecessor
-                $post = preg_replace('#([^/\.]+)/\./#', '\\1/', $post); // erase './'
-                if ($post == $full) {
-                    break; // nothing changed
-                }
-                $full = $post;
+        $content = preg_replace_callback('#(url\([\n\r\s\'"]*)([^\s\)\?\'"]+)#i', function ($match) use ($fileUrlDir) {
+            [ $_, $prefix, $relativePath ] = $match;
+            if ($relativePath[0] === '/' || false !== strpos($relativePath, '://')) {
+                return $prefix . $relativePath;
             }
+            $full = FilesystemPath::canonicalize($fileUrlDir . '/' . $relativePath);
             return $prefix . $full;
         }, $content);
         return $content;
diff --git a/tests/php/View/RequirementsTest.php b/tests/php/View/RequirementsTest.php
index 2728209b3..727d26eb0 100644
--- a/tests/php/View/RequirementsTest.php
+++ b/tests/php/View/RequirementsTest.php
@@ -164,6 +164,13 @@ class RequirementsTest extends SapphireTest
 
         $content = file_get_contents($combinedFilePath);
 
+        /* COMBINED CSS URL RESOLVER IGNORE FULL URLS */
+        $this->assertStringContainsString(
+            ".url { background: url(http://example.com/zero.gif); }",
+            $content,
+            'combined css url resolver ignore full urls'
+        );
+
         /* COMBINED CSS URL RESOLVER DECODED ONE DOT */
         $this->assertStringContainsString(
             ".p0 { background: url(/css/deep/deeper/zero.gif); }",
@@ -171,6 +178,20 @@ class RequirementsTest extends SapphireTest
             'combined css url resolver decoded one dot'
         );
 
+        /* COMBINED CSS URL RESOLVER DECODED NO DOTS */
+        $this->assertStringContainsString(
+            ".p0-plain { background: url(/css/deep/deeper/zero.gif); }",
+            $content,
+            'combined css url resolver decoded no dots'
+        );
+
+        /* COMBINED CSS URL RESOLVER DAMAGED A QUERYSTRING */
+        $this->assertStringContainsString(
+            ".p0-qs { background: url(/css/deep/deeper/zero.gif?some=param); }",
+            $content,
+            'combined css url resolver damaged a querystring'
+        );
+
         /* COMBINED CSS URL RESOLVER DECODED ONE DOT WITH SINGLE QUOTES */
         $this->assertStringContainsString(
             ".p0sq { background: url('/css/deep/deeper/zero-sq.gif'); }",
@@ -255,11 +276,18 @@ class RequirementsTest extends SapphireTest
             'combined css url resolver decoded 3 double-dot'
         );
 
-        /* COMBINED CSS URL RESOLVER DECODED 4 DOUBLE-DOT */
+        /* COMBINED CSS URL RESOLVER DECODED 4 DOUBLE-DOT WHEN ONLY 3 LEVELS AVAILABLE*/
         $this->assertStringContainsString(
-            ".p4 { background: url(/../four.gif); }",
+            ".p4 { background: url(/four.gif); }",
             $content,
-            'combined css url resolver decoded 4 double-dot'
+            'combined css url resolver decoded 4 double-dot when only 4 levels available'
+        );
+
+        /* COMBINED CSS URL RESOLVER MODIFIED AN ARBITRARY VALUE */
+        $this->assertStringContainsString(
+            ".weird { content: \"./keepme.gif\"; }",
+            $content,
+            'combined css url resolver modified an arbitrary value'
         );
     }
 
diff --git a/tests/php/View/SSViewerTest/public/css/deep/deeper/RequirementsTest_p.css b/tests/php/View/SSViewerTest/public/css/deep/deeper/RequirementsTest_p.css
index 291c8ea52..a499064ee 100644
--- a/tests/php/View/SSViewerTest/public/css/deep/deeper/RequirementsTest_p.css
+++ b/tests/php/View/SSViewerTest/public/css/deep/deeper/RequirementsTest_p.css
@@ -1,4 +1,7 @@
+.url { background: url(http://example.com/zero.gif); } /* don't touch this */
 .p0 { background: url(./zero.gif); }
+.p0-plain { background: url(zero.gif); }
+.p0-qs { background: url(./zero.gif?some=param); } /* keep the query string */
 .p0-nl { background: url(
   ./zero-nl.gif );
 }
@@ -20,3 +23,4 @@
 .p2dq { background: url("../../two-dq.gif"); }
 .p3 { background: url(../../../three.gif); }
 .p4 { background: url(../../../../four.gif); }
+.weird { content: "./keepme.gif"; }