diff --git a/components/style/properties/computed_value_flags.rs b/components/style/properties/computed_value_flags.rs
index dc9597e087b..cc7d9c94fb9 100644
--- a/components/style/properties/computed_value_flags.rs
+++ b/components/style/properties/computed_value_flags.rs
@@ -57,19 +57,24 @@ bitflags! {
         /// Whether the child explicitly inherits any reset property.
         const INHERITS_RESET_STYLE = 1 << 8;
 
-        /// Whether any value on our style is font-metric-dependent.
-        const DEPENDS_ON_FONT_METRICS = 1 << 9;
+        /// Whether any value on our style is font-metric-dependent on our
+        /// primary font.
+        const DEPENDS_ON_SELF_FONT_METRICS = 1 << 9;
+
+        /// Whether any value on our style is font-metric-dependent on the
+        /// primary font of our parent.
+        const DEPENDS_ON_INHERITED_FONT_METRICS = 1 << 10;
 
         /// Whether the style or any of the ancestors has a multicol style.
         ///
         /// Only used in Servo.
-        const CAN_BE_FRAGMENTED = 1 << 10;
+        const CAN_BE_FRAGMENTED = 1 << 11;
 
         /// Whether this style is the style of the document element.
-        const IS_ROOT_ELEMENT_STYLE = 1 << 11;
+        const IS_ROOT_ELEMENT_STYLE = 1 << 12;
 
         /// Whether this element is inside an `opacity: 0` subtree.
-        const IS_IN_OPACITY_ZERO_SUBTREE = 1 << 12;
+        const IS_IN_OPACITY_ZERO_SUBTREE = 1 << 13;
 
         /// Whether there are author-specified rules for border-* properties
         /// (except border-image-*), background-color, or background-image.
@@ -77,13 +82,13 @@ bitflags! {
         /// TODO(emilio): Maybe do include border-image, see:
         ///
         /// https://github.com/w3c/csswg-drafts/issues/4777#issuecomment-604424845
-        const HAS_AUTHOR_SPECIFIED_BORDER_BACKGROUND = 1 << 13;
+        const HAS_AUTHOR_SPECIFIED_BORDER_BACKGROUND = 1 << 14;
 
         /// Whether there are author-specified rules for padding-* properties.
         ///
         /// FIXME(emilio): Try to merge this with BORDER_BACKGROUND, see
         /// https://github.com/w3c/csswg-drafts/issues/4777
-        const HAS_AUTHOR_SPECIFIED_PADDING = 1 << 14;
+        const HAS_AUTHOR_SPECIFIED_PADDING = 1 << 15;
     }
 }
 
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 64a2e8cf5db..4fc841aea93 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -161,6 +161,10 @@ impl FontRelativeLength {
         }
 
         let reference_font_size = base_size.resolve(context);
+        let font_metrics_flag = match base_size {
+            FontBaseSize::CurrentStyle => ComputedValueFlags::DEPENDS_ON_SELF_FONT_METRICS,
+            FontBaseSize::InheritedStyle => ComputedValueFlags::DEPENDS_ON_INHERITED_FONT_METRICS,
+        };
         match *self {
             FontRelativeLength::Em(length) => {
                 if context.for_non_inherited_property.is_some() {
@@ -178,9 +182,7 @@ impl FontRelativeLength {
                 if context.for_non_inherited_property.is_some() {
                     context.rule_cache_conditions.borrow_mut().set_uncacheable();
                 }
-                context
-                    .builder
-                    .add_flags(ComputedValueFlags::DEPENDS_ON_FONT_METRICS);
+                context.builder.add_flags(font_metrics_flag);
                 // The x-height is an intrinsically horizontal metric.
                 let metrics =
                     query_font_metrics(context, base_size, FontMetricsOrientation::Horizontal);
@@ -199,9 +201,7 @@ impl FontRelativeLength {
                 if context.for_non_inherited_property.is_some() {
                     context.rule_cache_conditions.borrow_mut().set_uncacheable();
                 }
-                context
-                    .builder
-                    .add_flags(ComputedValueFlags::DEPENDS_ON_FONT_METRICS);
+                context.builder.add_flags(font_metrics_flag);
                 // https://drafts.csswg.org/css-values/#ch:
                 //
                 //     Equal to the used advance measure of the “0” (ZERO,