diff --git a/layout/style/BindingStyleRule.h b/layout/style/BindingStyleRule.h
index 91613db85aa2..96cf386d92e5 100644
--- a/layout/style/BindingStyleRule.h
+++ b/layout/style/BindingStyleRule.h
@@ -9,6 +9,7 @@
 #include "nscore.h"
 #include "nsStringGlue.h"
 #include "mozilla/css/Rule.h"
+#include "mozilla/NotNull.h"
 
 /**
  * Shared superclass for mozilla::css::StyleRule and mozilla::ServoStyleRule,
@@ -18,6 +19,7 @@
 class nsICSSDeclaration;
 
 namespace mozilla {
+class DeclarationBlock;
 namespace dom {
 class Element;
 }
@@ -54,6 +56,7 @@ public:
                                           uint32_t aSelectorIndex,
                                           const nsAString& aPseudo,
                                           bool* aMatches) = 0;
+  virtual NotNull<DeclarationBlock*> GetDeclarationBlock() const = 0;
 
   // WebIDL API
   // For GetSelectorText/SetSelectorText, we purposefully use a signature that
diff --git a/layout/style/ServoStyleRule.cpp b/layout/style/ServoStyleRule.cpp
index e4e6c5a43a60..1d7470eef037 100644
--- a/layout/style/ServoStyleRule.cpp
+++ b/layout/style/ServoStyleRule.cpp
@@ -298,4 +298,10 @@ ServoStyleRule::SelectorMatchesElement(Element* aElement,
   return NS_OK;
 }
 
+NotNull<DeclarationBlock*>
+ServoStyleRule::GetDeclarationBlock() const
+{
+  return WrapNotNull(mDecls.mDecls);
+}
+
 } // namespace mozilla
diff --git a/layout/style/ServoStyleRule.h b/layout/style/ServoStyleRule.h
index 30c0d640a08f..cf10aba03232 100644
--- a/layout/style/ServoStyleRule.h
+++ b/layout/style/ServoStyleRule.h
@@ -80,6 +80,7 @@ public:
                                   uint32_t aSelectorIndex,
                                   const nsAString& aPseudo,
                                   bool* aMatches) override;
+  NotNull<DeclarationBlock*> GetDeclarationBlock() const override;
 
   // WebIDL interface
   uint16_t Type() const final;
diff --git a/layout/style/StyleRule.cpp b/layout/style/StyleRule.cpp
index 6df39aeeba61..8c4b210523fd 100644
--- a/layout/style/StyleRule.cpp
+++ b/layout/style/StyleRule.cpp
@@ -1513,5 +1513,11 @@ StyleRule::SelectorMatchesElement(Element* aElement,
   return NS_OK;
 }
 
+NotNull<DeclarationBlock*>
+StyleRule::GetDeclarationBlock() const
+{
+  return WrapNotNull(mDeclaration);
+}
+
 } // namespace css
 } // namespace mozilla
diff --git a/layout/style/StyleRule.h b/layout/style/StyleRule.h
index 499638d296df..a9f436e55445 100644
--- a/layout/style/StyleRule.h
+++ b/layout/style/StyleRule.h
@@ -347,6 +347,7 @@ public:
                                   uint32_t aSelectorIndex,
                                   const nsAString& aPseudo,
                                   bool* aMatches) override;
+  mozilla::NotNull<DeclarationBlock*> GetDeclarationBlock() const override;
 
   // WebIDL interface
   uint16_t Type() const override;