diff --git a/components/style/properties/computed_value_flags.rs b/components/style/properties/computed_value_flags.rs
index 8ac90aee27f..f12760aa8b4 100644
--- a/components/style/properties/computed_value_flags.rs
+++ b/components/style/properties/computed_value_flags.rs
@@ -125,6 +125,11 @@ bitflags! {
         /// Whether the style evaluated the matched element to be an anchor of
         /// a relative selector.
         const ANCHORS_RELATIVE_SELECTOR = 1 << 25;
+
+        /// Whether the style uses container query units, in which case the style depends on the
+        /// container's size and we can't reuse it across cousins (without double-checking the
+        /// container at least).
+        const USES_CONTAINER_UNITS = 1 << 26;
     }
 }
 
diff --git a/components/style/sharing/mod.rs b/components/style/sharing/mod.rs
index a78eb724c5d..9e5b9603d77 100644
--- a/components/style/sharing/mod.rs
+++ b/components/style/sharing/mod.rs
@@ -877,10 +877,21 @@ impl<E: TElement> StyleSharingCache<E> {
             // NOTE(emilio): We only need to check name / namespace because we
             // do name-dependent style adjustments, like the display: contents
             // to display: none adjustment.
-            if target.namespace() != candidate.element.namespace() {
+            if target.namespace() != candidate.element.namespace() ||
+                target.local_name() != candidate.element.local_name()
+            {
                 return None;
             }
-            if target.local_name() != candidate.element.local_name() {
+            // When using container units, inherited style + rules matched aren't enough to
+            // determine whether the style is the same. We could actually do a full container
+            // lookup but for now we just check that our actual traversal parent matches.
+            if data
+                .styles
+                .primary()
+                .flags
+                .intersects(ComputedValueFlags::USES_CONTAINER_UNITS) &&
+                candidate.element.traversal_parent() != target.traversal_parent()
+            {
                 return None;
             }
             // Rule nodes and styles are computed independent of the element's actual visitedness,
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 45a3154fc0d..48928a8576d 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -7,6 +7,7 @@
 //! [length]: https://drafts.csswg.org/css-values/#lengths
 
 use super::{AllowQuirks, Number, Percentage, ToComputedValue};
+use crate::computed_value_flags::ComputedValueFlags;
 use crate::font_metrics::{FontMetrics, FontMetricsOrientation};
 use crate::parser::{Parse, ParserContext};
 use crate::values::computed::{self, CSSPixelLength, Context};
@@ -787,6 +788,8 @@ impl ContainerRelativeLength {
         if context.for_non_inherited_property {
             context.rule_cache_conditions.borrow_mut().set_uncacheable();
         }
+        context.builder.add_flags(ComputedValueFlags::USES_CONTAINER_UNITS);
+
         let size = context.get_container_size_query();
         let (factor, container_length) = match *self {
             Self::Cqw(v) => (v, size.get_container_width(context)),