diff --git a/components/style/gecko/media_features.rs b/components/style/gecko/media_features.rs
index 321669ce1af..ed0dac47795 100644
--- a/components/style/gecko/media_features.rs
+++ b/components/style/gecko/media_features.rs
@@ -17,18 +17,6 @@ use crate::Atom;
 use app_units::Au;
 use euclid::default::Size2D;
 
-fn viewport_size(device: &Device) -> Size2D<Au> {
-    if let Some(pc) = device.pres_context() {
-        if pc.mIsRootPaginatedDocument() != 0 {
-            // We want the page size, including unprintable areas and margins.
-            // FIXME(emilio, bug 1414600): Not quite!
-            let area = &pc.mPageSize;
-            return Size2D::new(Au(area.width), Au(area.height));
-        }
-    }
-    device.au_viewport_size()
-}
-
 fn device_size(device: &Device) -> Size2D<Au> {
     let mut width = 0;
     let mut height = 0;
@@ -47,7 +35,7 @@ fn eval_width(
     RangeOrOperator::evaluate(
         range_or_operator,
         value.map(Au::from),
-        viewport_size(device).width,
+        device.au_viewport_size().width,
     )
 }
 
@@ -73,7 +61,7 @@ fn eval_height(
     RangeOrOperator::evaluate(
         range_or_operator,
         value.map(Au::from),
-        viewport_size(device).height,
+        device.au_viewport_size().height,
     )
 }
 
@@ -115,7 +103,7 @@ fn eval_aspect_ratio(
     query_value: Option<Ratio>,
     range_or_operator: Option<RangeOrOperator>,
 ) -> bool {
-    eval_aspect_ratio_for(device, query_value, range_or_operator, viewport_size)
+    eval_aspect_ratio_for(device, query_value, range_or_operator, Device::au_viewport_size)
 }
 
 /// https://drafts.csswg.org/mediaqueries-4/#device-aspect-ratio
@@ -168,7 +156,7 @@ where
 
 /// https://drafts.csswg.org/mediaqueries-4/#orientation
 fn eval_orientation(device: &Device, value: Option<Orientation>) -> bool {
-    eval_orientation_for(device, value, viewport_size)
+    eval_orientation_for(device, value, Device::au_viewport_size)
 }
 
 /// FIXME: There's no spec for `-moz-device-orientation`.
diff --git a/components/style/gecko/media_queries.rs b/components/style/gecko/media_queries.rs
index 663acae7b6e..cf28002e621 100644
--- a/components/style/gecko/media_queries.rs
+++ b/components/style/gecko/media_queries.rs
@@ -19,7 +19,7 @@ use cssparser::RGBA;
 use euclid::default::Size2D;
 use euclid::{Scale, SideOffsets2D};
 use servo_arc::Arc;
-use std::fmt;
+use std::{cmp, fmt};
 use std::sync::atomic::{AtomicBool, AtomicU32, AtomicUsize, Ordering};
 use style_traits::viewport::ViewportConstraints;
 use style_traits::{CSSPixel, DevicePixel};
@@ -223,12 +223,29 @@ impl Device {
         MediaType(CustomIdent(unsafe { Atom::from_raw(medium_to_use) }))
     }
 
+    // It may make sense to account for @page rule margins here somehow, however
+    // it's not clear how that'd work, see:
+    // https://github.com/w3c/csswg-drafts/issues/5437
+    fn page_size_minus_default_margin(&self, pc: &structs::nsPresContext) -> Size2D<Au> {
+        debug_assert!(pc.mIsRootPaginatedDocument() != 0);
+        let area = &pc.mPageSize;
+        let margin = &pc.mDefaultPageMargin;
+        let width = area.width - margin.left - margin.right;
+        let height = area.height - margin.top - margin.bottom;
+        Size2D::new(Au(cmp::max(width, 0)), Au(cmp::max(height, 0)))
+    }
+
     /// Returns the current viewport size in app units.
     pub fn au_viewport_size(&self) -> Size2D<Au> {
         let pc = match self.pres_context() {
             Some(pc) => pc,
             None => return Size2D::new(Au(0), Au(0)),
         };
+
+        if pc.mIsRootPaginatedDocument() != 0 {
+            return self.page_size_minus_default_margin(pc);
+        }
+
         let area = &pc.mVisibleArea;
         Size2D::new(Au(area.width), Au(area.height))
     }
@@ -237,11 +254,15 @@ impl Device {
     /// used for viewport unit resolution.
     pub fn au_viewport_size_for_viewport_unit_resolution(&self) -> Size2D<Au> {
         self.used_viewport_size.store(true, Ordering::Relaxed);
-
         let pc = match self.pres_context() {
             Some(pc) => pc,
             None => return Size2D::new(Au(0), Au(0)),
         };
+
+        if pc.mIsRootPaginatedDocument() != 0 {
+            return self.page_size_minus_default_margin(pc)
+        }
+
         let size = &pc.mSizeForViewportUnits;
         Size2D::new(Au(size.width), Au(size.height))
     }