diff --git a/layout/style/ComputedStyle.cpp b/layout/style/ComputedStyle.cpp
index 64c3d4640b8f..83057105a109 100644
--- a/layout/style/ComputedStyle.cpp
+++ b/layout/style/ComputedStyle.cpp
@@ -448,6 +448,8 @@ ComputedStyle::GetCachedLazyPseudoStyle(CSSPseudoElementType aPseudo) const
   return mCachedInheritingStyles.Lookup(nsCSSPseudoElements::GetPseudoAtom(aPseudo));
 }
 
+MOZ_DEFINE_MALLOC_ENCLOSING_SIZE_OF(ServoComputedValuesMallocEnclosingSizeOf)
+
 void
 ComputedStyle::AddSizeOfIncludingThis(nsWindowSizes& aSizes,
                                       size_t* aCVsSize) const
diff --git a/layout/style/ComputedStyle.h b/layout/style/ComputedStyle.h
index ea9a5b36f396..dce4cb468a2c 100644
--- a/layout/style/ComputedStyle.h
+++ b/layout/style/ComputedStyle.h
@@ -34,8 +34,6 @@ extern "C" {
   void Gecko_ComputedStyle_Destroy(mozilla::ComputedStyle*);
 }
 
-MOZ_DEFINE_MALLOC_ENCLOSING_SIZE_OF(ServoComputedValuesMallocEnclosingSizeOf)
-
 /**
  * A ComputedStyle represents the computed style data for an element.  The
  * computed style data are stored in a set of structs (see nsStyleStruct.h) that