diff --git a/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/animation-timing-function.html b/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/animation-timing-function.html
index b66d64c9b9a1..eb9af36a85ae 100644
--- a/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/animation-timing-function.html
+++ b/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/animation-timing-function.html
@@ -19,8 +19,18 @@ runListValuedPropertyTests('animation-timing-function', [
   { syntax: 'ease-in' },
   { syntax: 'ease-out' },
   { syntax: 'ease-in-out' },
-  { syntax: 'step-start' },
-  { syntax: 'step-end' },
+  {
+    syntax: 'step-start',
+    computed: (_, result) => {
+      assert_equals(result.toString(), 'steps(1, start)');
+    }
+  },
+  {
+    syntax: 'step-end',
+    computed: (_, result) => {
+      assert_equals(result.toString(), 'steps(1)');
+    }
+  },
 ]);
 
 runUnsupportedPropertyTests('animation-timing-function', [
diff --git a/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/transition-timing-function.html b/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/transition-timing-function.html
index 5d3260f7a51b..a4dbfc19330e 100644
--- a/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/transition-timing-function.html
+++ b/testing/web-platform/tests/css/css-typed-om/the-stylepropertymap/properties/transition-timing-function.html
@@ -19,8 +19,18 @@ runListValuedPropertyTests('transition-timing-function', [
   { syntax: 'ease-in' },
   { syntax: 'ease-out' },
   { syntax: 'ease-in-out' },
-  { syntax: 'step-start' },
-  { syntax: 'step-end' },
+  {
+    syntax: 'step-start',
+    computed: (_, result) => {
+      assert_equals(result.toString(), 'steps(1, start)');
+    }
+  },
+  {
+    syntax: 'step-end',
+    computed: (_, result) => {
+      assert_equals(result.toString(), 'steps(1)');
+    }
+  },
 ]);
 
 runUnsupportedPropertyTests('transition-timing-function', [