--- a/layout/style/ServoBindings.cpp
+++ b/layout/style/ServoBindings.cpp
@@ -1797,44 +1797,43 @@ Gecko_EnsureImageLayersLength(nsStyleIma
 
   aLayers->mLayers.EnsureLengthAtLeast(aLen);
 
   for (size_t i = oldLength; i < aLen; ++i) {
     aLayers->mLayers[i].Initialize(aLayerType);
   }
 }
 
+template <typename StyleType>
+static void
+EnsureStyleAutoArrayLength(StyleType* aArray, size_t aLen)
+{
+  size_t oldLength = aArray->Length();
+
+  aArray->EnsureLengthAtLeast(aLen);
+
+  for (size_t i = oldLength; i < aLen; ++i) {
+    (*aArray)[i].SetInitialValues();
+  }
+}
+
 void
 Gecko_EnsureStyleAnimationArrayLength(void* aArray, size_t aLen)
 {
   auto base =
     static_cast<nsStyleAutoArray<StyleAnimation>*>(aArray);
-
-  size_t oldLength = base->Length();
-
-  base->EnsureLengthAtLeast(aLen);
-
-  for (size_t i = oldLength; i < aLen; ++i) {
-    (*base)[i].SetInitialValues();
-  }
+  EnsureStyleAutoArrayLength(base, aLen);
 }
 
 void
 Gecko_EnsureStyleTransitionArrayLength(void* aArray, size_t aLen)
 {
   auto base =
     reinterpret_cast<nsStyleAutoArray<StyleTransition>*>(aArray);
-
-  size_t oldLength = base->Length();
-
-  base->EnsureLengthAtLeast(aLen);
-
-  for (size_t i = oldLength; i < aLen; ++i) {
-    (*base)[i].SetInitialValues();
-  }
+  EnsureStyleAutoArrayLength(base, aLen);
 }
 
 void
 Gecko_ClearWillChange(nsStyleDisplay* aDisplay, size_t aLength)
 {
   aDisplay->mWillChange.Clear();
   aDisplay->mWillChange.SetCapacity(aLength);
 }