diff --git a/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp b/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
index cea99783d8..6f73183be3 100644
--- a/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
+++ b/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
@@ -297,6 +297,13 @@ static void serialize_a_math_function(StringBuilder& builder, CalculationNode co
         return;
     }
 
+    // AD-HOC: A non-math function like sibling-index() or anchor() has no calc() wrapper. Serialize it directly per
+    //         the normal rules for it.
+    if (fn.type() == CalculationNode::Type::NonMathFunction) {
+        serialize_a_calculation_tree(builder, fn, context, serialization_mode, EmitOuterParentheses::No);
+        return;
+    }
+
     // 3. If the calculation tree’s root node is a numeric value, or a calc-operator node, let s be a string initially
     //    containing "calc(".
     //    Otherwise, let s be a string initially containing the name of the root node, lowercased (such as "sin" or
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.txt
index 8273808df2..818e021ecc 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.txt
@@ -1,15 +1,53 @@
 Harness status: OK
 
-Found 10 tests
+Found 47 tests
 
-10 Pass
+45 Pass
+2 Fail
 Pass	e.style['left'] = "calc(1px * sibling-index())" should set the property value
 Pass	e.style['left'] = "calc(1px * sibling-index( ))" should set the property value
-Pass	e.style['z-index'] = "sibling-index()" should set the property value
+Pass	e.style['left'] = "calc(1em * sibling-index())" should set the property value
+Pass	e.style['left'] = "calc(1rem * sibling-count())" should set the property value
+Pass	e.style['left'] = "calc(1vh * sibling-index())" should set the property value
+Pass	e.style['left'] = "calc(1ch * sibling-count())" should set the property value
+Pass	e.style['left'] = "calc(1% * sibling-index())" should set the property value
+Pass	e.style['left'] = "calc(5% * sibling-count())" should set the property value
 Pass	e.style['left'] = "calc(1px * sibling-index(100px))" should not set the property value
 Pass	e.style['left'] = "calc(1px * sibling-index(1))" should not set the property value
-Pass	e.style['left'] = "calc(1px * sibling-count())" should set the property value
-Pass	e.style['left'] = "calc(1px * sibling-count( ))" should set the property value
+Pass	e.style['left'] = "calc(10 * sibling-index())" should not set the property value
+Pass	e.style['rotate'] = "calc(10deg * sibling-index())" should set the property value
+Fail	e.style['rotate'] = "calc(sibling-index() * 2rad * pi)" should set the property value
+Pass	e.style['rotate'] = "calc(1turn * sibling-count())" should set the property value
+Fail	e.style['rotate'] = "calc(sibling-count() * 1rad * pi)" should set the property value
+Pass	e.style['rotate'] = "calc(1px * sibling-index())" should not set the property value
+Pass	e.style['rotate'] = "calc(1s * sibling-index())" should not set the property value
+Pass	e.style['z-index'] = "sibling-index()" should set the property value
 Pass	e.style['z-index'] = "sibling-count()" should set the property value
-Pass	e.style['left'] = "calc(1px * sibling-count(100px))" should not set the property value
-Pass	e.style['left'] = "calc(1px * sibling-count(1))" should not set the property value
\ No newline at end of file
+Pass	e.style['z-index'] = "calc(2 * sibling-index())" should set the property value
+Pass	e.style['z-index'] = "calc(sibling-index())" should set the property value
+Pass	e.style['z-index'] = "calc(sibling-count())" should set the property value
+Pass	e.style['z-index'] = "sibling-index(100px)" should not set the property value
+Pass	e.style['z-index'] = "sibling-count(1)" should not set the property value
+Pass	e.style['opacity'] = "calc(0.1 * sibling-index())" should set the property value
+Pass	e.style['opacity'] = "calc(0.5 * sibling-count())" should set the property value
+Pass	e.style['scale'] = "calc(2 * sibling-index())" should set the property value
+Pass	e.style['scale'] = "calc(0.5 * sibling-count())" should set the property value
+Pass	e.style['opacity'] = "calc(1ms * sibling-index())" should not set the property value
+Pass	e.style['opacity'] = "calc(1px * sibling-count())" should not set the property value
+Pass	e.style['animation-duration'] = "calc(1s * sibling-index())" should set the property value
+Pass	e.style['animation-duration'] = "calc(1s * sibling-count( ))" should set the property value
+Pass	e.style['animation-duration'] = "calc(100ms * sibling-count())" should set the property value
+Pass	e.style['animation-duration'] = "calc(0.5s * sibling-index())" should set the property value
+Pass	e.style['animation-duration'] = "calc(250ms * sibling-index())" should set the property value
+Pass	e.style['animation-duration'] = "calc(1px * sibling-index())" should not set the property value
+Pass	e.style['animation-duration'] = "calc(1deg * sibling-index())" should not set the property value
+Pass	e.style['color'] = "color(srgb calc(0.1 * sibling-index()) 0.5 0.5)" should set the property value
+Pass	e.style['color'] = "color(srgb 0 calc(0.1 * sibling-count()) 0.5)" should set the property value
+Pass	e.style['color'] = "color(srgb 0 0 calc(0.1 * sibling-index()))" should set the property value
+Pass	e.style['color'] = "color(srgb 0.5 0.5 0.5 / calc(0.1 * sibling-count()))" should set the property value
+Pass	e.style['color'] = "oklch(calc(0.1 * sibling-index()) 0.2 180)" should set the property value
+Pass	e.style['color'] = "oklch(0.5 calc(0.05 * sibling-count()) 180)" should set the property value
+Pass	e.style['color'] = "oklch(0.5 0.2 calc(30deg * sibling-index()))" should set the property value
+Pass	e.style['color'] = "oklch(0.5 0.2 180 / calc(0.1 * sibling-index()))" should set the property value
+Pass	e.style['color'] = "color(srgb calc(1px * sibling-index()) 0 0)" should not set the property value
+Pass	e.style['color'] = "oklch(calc(1px * sibling-index()) 0 0)" should not set the property value
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.html b/Tests/LibWeb/Text/input/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.html
index b10601a6c4..a428873a6a 100644
--- a/Tests/LibWeb/Text/input/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.html
+++ b/Tests/LibWeb/Text/input/wpt-import/css/css-values/tree-counting/calc-sibling-function-parsing.html
@@ -9,19 +9,70 @@
 </head>
 <body>
   <script>
+// <length>
 test_valid_value('left', 'calc(1px * sibling-index())');
 test_valid_value('left', 'calc(1px * sibling-index( ))', 'calc(1px * sibling-index())');
-test_valid_value('z-index', 'sibling-index()');
+test_valid_value('left', 'calc(1em * sibling-index())');
+test_valid_value('left', 'calc(1rem * sibling-count())');
+test_valid_value('left', 'calc(1vh * sibling-index())');
+test_valid_value('left', 'calc(1ch * sibling-count())');
+test_valid_value('left', 'calc(1% * sibling-index())');
+test_valid_value('left', 'calc(5% * sibling-count())');
 
 test_invalid_value('left', 'calc(1px * sibling-index(100px))');
 test_invalid_value('left', 'calc(1px * sibling-index(1))');
+test_invalid_value('left', 'calc(10 * sibling-index())');
 
-test_valid_value('left', 'calc(1px * sibling-count())');
-test_valid_value('left', 'calc(1px * sibling-count( ))', 'calc(1px * sibling-count())');
+// <angle>
+test_valid_value('rotate', 'calc(10deg * sibling-index())');
+test_valid_value('rotate', 'calc(sibling-index() * 2rad * pi)', 'calc(360deg * sibling-index())');
+test_valid_value('rotate', 'calc(1turn * sibling-count())', 'calc(360deg * sibling-count())');
+test_valid_value('rotate', 'calc(sibling-count() * 1rad * pi)', 'calc(180deg * sibling-count())');
+
+test_invalid_value('rotate', 'calc(1px * sibling-index())');
+test_invalid_value('rotate', 'calc(1s * sibling-index())');
+
+//  <integer> (which accepts these functions without calc())
+test_valid_value('z-index', 'sibling-index()');
 test_valid_value('z-index', 'sibling-count()');
+test_valid_value('z-index', 'calc(2 * sibling-index())');
+test_valid_value('z-index', 'calc(sibling-index())', 'sibling-index()');
+test_valid_value('z-index', 'calc(sibling-count())', 'sibling-count()');
 
-test_invalid_value('left', 'calc(1px * sibling-count(100px))');
-test_invalid_value('left', 'calc(1px * sibling-count(1))');
+test_invalid_value('z-index', 'sibling-index(100px)');
+test_invalid_value('z-index', 'sibling-count(1)');
+
+// <number>
+test_valid_value('opacity', 'calc(0.1 * sibling-index())');
+test_valid_value('opacity', 'calc(0.5 * sibling-count())');
+test_valid_value('scale', 'calc(2 * sibling-index())');
+test_valid_value('scale', 'calc(0.5 * sibling-count())');
+
+test_invalid_value('opacity', 'calc(1ms * sibling-index())');
+test_invalid_value('opacity', 'calc(1px * sibling-count())');
+
+// <time>
+test_valid_value('animation-duration', 'calc(1s * sibling-index())');
+test_valid_value('animation-duration', 'calc(1s * sibling-count( ))', 'calc(1s * sibling-count())');
+test_valid_value('animation-duration', 'calc(100ms * sibling-count())', 'calc(0.1s * sibling-count())');
+test_valid_value('animation-duration', 'calc(0.5s * sibling-index())');
+test_valid_value('animation-duration', 'calc(250ms * sibling-index())', 'calc(0.25s * sibling-index())');
+
+test_invalid_value('animation-duration', 'calc(1px * sibling-index())');
+test_invalid_value('animation-duration', 'calc(1deg * sibling-index())');
+
+// <color> functions
+test_valid_value('color', 'color(srgb calc(0.1 * sibling-index()) 0.5 0.5)');
+test_valid_value('color', 'color(srgb 0 calc(0.1 * sibling-count()) 0.5)');
+test_valid_value('color', 'color(srgb 0 0 calc(0.1 * sibling-index()))');
+test_valid_value('color', 'color(srgb 0.5 0.5 0.5 / calc(0.1 * sibling-count()))');
+test_valid_value('color', 'oklch(calc(0.1 * sibling-index()) 0.2 180)');
+test_valid_value('color', 'oklch(0.5 calc(0.05 * sibling-count()) 180)');
+test_valid_value('color', 'oklch(0.5 0.2 calc(30deg * sibling-index()))');
+test_valid_value('color', 'oklch(0.5 0.2 180 / calc(0.1 * sibling-index()))');
+
+test_invalid_value('color', 'color(srgb calc(1px * sibling-index()) 0 0)');
+test_invalid_value('color', 'oklch(calc(1px * sibling-index()) 0 0)');
   </script>
 </body>
 </html>