diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 0ef6568c669..1eeaeee316a 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -166,9 +166,12 @@ pub struct Context<'a> {
     #[cfg(feature = "servo")]
     pub cached_system_font: Option<()>,
 
-    /// Whether or not we are computing the media list in a media query
+    /// Whether or not we are computing the media list in a media query.
     pub in_media_query: bool,
 
+    /// Whether or not we are computing the container query condition.
+    pub in_container_query: bool,
+
     /// The quirks mode of this context.
     pub quirks_mode: QuirksMode,
 
@@ -215,6 +218,7 @@ impl<'a> Context<'a> {
             builder: StyleBuilder::for_inheritance(device, None, None),
             cached_system_font: None,
             in_media_query: true,
+            in_container_query: true,
             quirks_mode,
             for_smil_animation: false,
             container_info: None,
@@ -248,7 +252,8 @@ impl<'a> Context<'a> {
         let context = Context {
             builder: StyleBuilder::for_inheritance(device, style, None),
             cached_system_font: None,
-            in_media_query: true,
+            in_media_query: false,
+            in_container_query: true,
             quirks_mode,
             for_smil_animation: false,
             container_info,
@@ -271,6 +276,7 @@ impl<'a> Context<'a> {
             builder,
             cached_system_font: None,
             in_media_query: false,
+            in_container_query: false,
             quirks_mode,
             container_info: None,
             for_smil_animation: false,
@@ -292,6 +298,7 @@ impl<'a> Context<'a> {
             builder,
             cached_system_font: None,
             in_media_query: false,
+            in_container_query: false,
             quirks_mode,
             container_info: None,
             for_smil_animation,
@@ -344,7 +351,7 @@ impl<'a> Context<'a> {
             vertical,
             font,
             size,
-            self.in_media_query,
+            self.in_media_or_container_query(),
             retrieve_math_scales,
         )
     }
@@ -359,6 +366,11 @@ impl<'a> Context<'a> {
             .au_viewport_size_for_viewport_unit_resolution(variant)
     }
 
+    /// Whether we're in a media or container query.
+    pub fn in_media_or_container_query(&self) -> bool {
+        self.in_media_query || self.in_container_query
+    }
+
     /// The default computed style we're getting our reset style from.
     pub fn default_style(&self) -> &ComputedValues {
         self.builder.default_style()
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 523ae05354a..7ae816aebd2 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -264,7 +264,7 @@ impl FontRelativeLength {
                 //     element, the rem units refer to the property's initial
                 //     value.
                 //
-                let reference_size = if context.builder.is_root_element || context.in_media_query {
+                let reference_size = if context.builder.is_root_element || context.in_media_or_container_query() {
                     reference_font_size
                 } else {
                     context.device().root_font_size()