diff --git a/components/style/properties/longhand/box.mako.rs b/components/style/properties/longhand/box.mako.rs
index 851beb6267c..95f868af743 100644
--- a/components/style/properties/longhand/box.mako.rs
+++ b/components/style/properties/longhand/box.mako.rs
@@ -2096,8 +2096,10 @@ ${helpers.single_keyword("transform-style",
             const LAYOUT = 0x02,
             const STYLE = 0x04,
             const PAINT = 0x08,
-            const STRICT = SIZE.bits | LAYOUT.bits | STYLE.bits | PAINT.bits,
-            const CONTENT = LAYOUT.bits | STYLE.bits | PAINT.bits,
+            const STRICT = 0x10,
+            const STRICT_BITS = SIZE.bits | LAYOUT.bits | STYLE.bits | PAINT.bits,
+            const CONTENT = 0x20,
+            const CONTENT_BITS = LAYOUT.bits | STYLE.bits | PAINT.bits,
         }
     }
 
@@ -2148,11 +2150,11 @@ ${helpers.single_keyword("transform-style",
             return Ok(result)
         }
         if input.try(|input| input.expect_ident_matching("strict")).is_ok() {
-            result.insert(STRICT);
+            result.insert(STRICT | STRICT_BITS);
             return Ok(result)
         }
         if input.try(|input| input.expect_ident_matching("content")).is_ok() {
-            result.insert(CONTENT);
+            result.insert(CONTENT | CONTENT_BITS);
             return Ok(result)
         }
 
diff --git a/tests/unit/style/parsing/containment.rs b/tests/unit/style/parsing/containment.rs
index d4cffe9f1a5..2ef6a08659e 100644
--- a/tests/unit/style/parsing/containment.rs
+++ b/tests/unit/style/parsing/containment.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use parsing::parse;
+use style_traits::ToCss;
 
 #[test]
 fn contain_longhand_should_parse_correctly() {
@@ -13,11 +14,20 @@ fn contain_longhand_should_parse_correctly() {
     assert_eq!(none, SpecifiedValue::empty());
 
     let strict = parse_longhand!(contain, "strict");
-    assert_eq!(strict, contain::STRICT);
+    assert_eq!(strict, contain::STRICT | contain::STRICT_BITS);
+
+    let strict = parse_longhand!(contain, "content");
+    assert_eq!(strict, contain::CONTENT | contain::CONTENT_BITS);
 
     let style_paint = parse_longhand!(contain, "style paint");
     assert_eq!(style_paint, contain::STYLE | contain::PAINT);
 
+    assert_roundtrip_with_context!(contain::parse, "strict");
+    assert_roundtrip_with_context!(contain::parse, "size layout style paint");
+
+    assert_roundtrip_with_context!(contain::parse, "content");
+    assert_roundtrip_with_context!(contain::parse, "layout style paint");
+
     // Assert that the `2px` is not consumed, which would trigger parsing failure in real use
     assert_parser_exhausted!(contain::parse, "layout 2px", false);
 }