diff --git a/components/hashglobe/src/hash_set.rs b/components/hashglobe/src/hash_set.rs
index 694e01c46eb..ef373ae3710 100644
--- a/components/hashglobe/src/hash_set.rs
+++ b/components/hashglobe/src/hash_set.rs
@@ -17,6 +17,8 @@ use std::ops::{BitAnd, BitOr, BitXor, Sub};
 use super::hash_map::{self, HashMap, Keys, RandomState};
 use super::Recover;
 
+use crate::FailedAllocationError;
+
 // Future Optimization (FIXME!)
 // =============================
 //
@@ -589,6 +591,12 @@ where
         self.map.insert(value, ()).is_none()
     }
 
+    /// Fallible version of `insert`.
+    #[inline]
+    pub fn try_insert(&mut self, value: T) -> Result<bool, FailedAllocationError> {
+        Ok(self.map.try_insert(value, ())?.is_none())
+    }
+
     /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
     /// one. Returns the replaced value.
     pub fn replace(&mut self, value: T) -> Option<T> {
diff --git a/components/style/invalidation/stylesheets.rs b/components/style/invalidation/stylesheets.rs
index 1359cce6054..244366af21d 100644
--- a/components/style/invalidation/stylesheets.rs
+++ b/components/style/invalidation/stylesheets.rs
@@ -8,6 +8,7 @@
 #![deny(unsafe_code)]
 
 use crate::dom::{TDocument, TElement, TNode};
+use crate::hash::HashSet;
 use crate::invalidation::element::element_wrapper::{ElementSnapshot, ElementWrapper};
 use crate::invalidation::element::restyle_hints::RestyleHint;
 use crate::media_queries::Device;
@@ -17,9 +18,12 @@ use crate::stylesheets::{CssRule, StylesheetInDocument};
 use crate::Atom;
 use crate::CaseSensitivityExt;
 use crate::LocalName as SelectorLocalName;
-use fxhash::FxHashSet;
+use fxhash::FxHasher;
 use selectors::attr::CaseSensitivity;
 use selectors::parser::{Component, LocalName, Selector};
+use std::hash::BuildHasherDefault;
+
+type FxHashSet<K> = HashSet<K, BuildHasherDefault<FxHasher>>;
 
 /// A style sheet invalidation represents a kind of element or subtree that may
 /// need to be restyled. Whether it represents a whole subtree or just a single
@@ -400,16 +404,21 @@ impl StylesheetInvalidationSet {
 
         if let Some(s) = subtree_invalidation {
             debug!(" > Found subtree invalidation: {:?}", s);
-            self.invalid_scopes.insert(s);
-        } else if let Some(s) = element_invalidation {
-            debug!(" > Found element invalidation: {:?}", s);
-            self.invalid_elements.insert(s);
-        } else {
-            // The selector was of a form that we can't handle. Any element
-            // could match it, so let's just bail out.
-            debug!(" > Can't handle selector, marking fully invalid");
-            self.fully_invalid = true;
+            if self.invalid_scopes.try_insert(s).is_ok() {
+                return;
+            }
         }
+        if let Some(s) = element_invalidation {
+            debug!(" > Found element invalidation: {:?}", s);
+            if self.invalid_elements.try_insert(s).is_ok() {
+                return;
+            }
+        }
+
+        // The selector was of a form that we can't handle. Any element could
+        // match it, so let's just bail out.
+        debug!(" > Can't handle selector or OOMd, marking fully invalid");
+        self.fully_invalid = true;
     }
 
     /// Collects invalidations for a given CSS rule.