diff --git a/caps/BasePrincipal.h b/caps/BasePrincipal.h
index 132c53fc347a..4f74badb205d 100644
--- a/caps/BasePrincipal.h
+++ b/caps/BasePrincipal.h
@@ -256,6 +256,16 @@ class BasePrincipal : public nsJSPrincipals {
   void FinishInit(BasePrincipal* aOther,
                   const OriginAttributes& aOriginAttributes);
 
+  // KeyValT holds a principal subtype-specific key value and the associated
+  // parsed value after JSON parsing.
+  template<typename SerializedKey>
+  struct KeyValT
+  {
+    bool valueWasSerialized;
+    nsCString value;
+    SerializedKey key;
+  };
+
  private:
   static already_AddRefed<BasePrincipal> CreateContentPrincipal(
       nsIURI* aURI, const OriginAttributes& aAttrs,
diff --git a/caps/ContentPrincipal.h b/caps/ContentPrincipal.h
index 0e7dac44d7be..653ee8e25de0 100644
--- a/caps/ContentPrincipal.h
+++ b/caps/ContentPrincipal.h
@@ -60,14 +60,8 @@ class ContentPrincipal final : public BasePrincipal {
   virtual nsresult PopulateJSONObject(Json::Value& aObject) override;
   // Serializable keys are the valid enum fields the serialization supports
   enum SerializableKeys { eURI = 0, eDomain, eSuffix, eMax = eSuffix };
-  // KeyVal is a lightweight storage that passes
-  // SerializableKeys and values after JSON parsing in the BasePrincipal to
-  // FromProperties
-  struct KeyVal {
-    bool valueWasSerialized;
-    nsCString value;
-    SerializableKeys key;
-  };
+  typedef mozilla::BasePrincipal::KeyValT<SerializableKeys> KeyVal;
+
   static already_AddRefed<BasePrincipal> FromProperties(
       nsTArray<ContentPrincipal::KeyVal>& aFields);
 
diff --git a/caps/ExpandedPrincipal.h b/caps/ExpandedPrincipal.h
index 98ff40437f4d..71dcceb1fd5e 100644
--- a/caps/ExpandedPrincipal.h
+++ b/caps/ExpandedPrincipal.h
@@ -63,14 +63,8 @@ class ExpandedPrincipal : public nsIExpandedPrincipal,
   virtual nsresult PopulateJSONObject(Json::Value& aObject) override;
   // Serializable keys are the valid enum fields the serialization supports
   enum SerializableKeys { eSpecs = 0, eSuffix, eMax = eSuffix };
-  // KeyVal is a lightweight storage that passes
-  // SerializableKeys and values after JSON parsing in the BasePrincipal to
-  // FromProperties
-  struct KeyVal {
-    bool valueWasSerialized;
-    nsCString value;
-    SerializableKeys key;
-  };
+  typedef mozilla::BasePrincipal::KeyValT<SerializableKeys> KeyVal;
+
   static already_AddRefed<BasePrincipal> FromProperties(
       nsTArray<ExpandedPrincipal::KeyVal>& aFields);
 
diff --git a/caps/NullPrincipal.h b/caps/NullPrincipal.h
index 09f09581bed4..268555119b54 100644
--- a/caps/NullPrincipal.h
+++ b/caps/NullPrincipal.h
@@ -87,14 +87,8 @@ class NullPrincipal final : public BasePrincipal {
 
   // Serializable keys are the valid enum fields the serialization supports
   enum SerializableKeys { eSpec = 0, eSuffix, eMax = eSuffix };
-  // KeyVal is a lightweight storage that passes
-  // SerializableKeys and values after JSON parsing in the BasePrincipal to
-  // FromProperties
-  struct KeyVal {
-    bool valueWasSerialized;
-    nsCString value;
-    SerializableKeys key;
-  };
+  typedef mozilla::BasePrincipal::KeyValT<SerializableKeys> KeyVal;
+
   static already_AddRefed<BasePrincipal> FromProperties(
       nsTArray<NullPrincipal::KeyVal>& aFields);