diff --git a/components/style/stylesheets/container_rule.rs b/components/style/stylesheets/container_rule.rs
index f4d652e6e45..991f06e2acb 100644
--- a/components/style/stylesheets/container_rule.rs
+++ b/components/style/stylesheets/container_rule.rs
@@ -375,9 +375,7 @@ pub struct ContainerSizeQueryResult {
 impl ContainerSizeQueryResult {
     fn get_viewport_size(context: &Context) -> Size2D<Au> {
         use crate::values::specified::ViewportVariant;
-        context
-            .device()
-            .au_viewport_size_for_viewport_unit_resolution(ViewportVariant::Small)
+        context.viewport_size_for_viewport_unit_resolution(ViewportVariant::Small)
     }
 
     fn get_logical_viewport_size(context: &Context) -> LogicalSize<Au> {
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index d7c4281fd33..29bed80d926 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -5,7 +5,6 @@
 //! `<length>` computed values, and related ones.
 
 use super::{Context, Number, ToComputedValue};
-use crate::computed_value_flags::ComputedValueFlags;
 use crate::values::animated::ToAnimatedValue;
 use crate::values::computed::NonNegativeNumber;
 use crate::values::generics::length as generics;
@@ -53,16 +52,9 @@ impl specified::NoCalcLength {
                 length.to_computed_value(context, base_size)
             },
             specified::NoCalcLength::ViewportPercentage(length) => {
-                context
-                    .builder
-                    .add_flags(ComputedValueFlags::USES_VIEWPORT_UNITS);
                 length.to_computed_value(context)
             },
             specified::NoCalcLength::ContainerRelative(length) => {
-                // Fallback uses small viewport size.
-                context
-                    .builder
-                    .add_flags(ComputedValueFlags::USES_VIEWPORT_UNITS);
                 length.to_computed_value(context)
             },
             specified::NoCalcLength::ServoCharacterWidth(length) => {
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 1eeaeee316a..a38bf049ad0 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -361,6 +361,8 @@ impl<'a> Context<'a> {
         &self,
         variant: ViewportVariant,
     ) -> default::Size2D<Au> {
+        self.builder
+            .add_flags(ComputedValueFlags::USES_VIEWPORT_UNITS);
         self.builder
             .device
             .au_viewport_size_for_viewport_unit_resolution(variant)