diff --git a/flang/lib/evaluate/expression.cc b/flang/lib/evaluate/expression.cc
index b961e32762b2..a89816a55d1f 100644
--- a/flang/lib/evaluate/expression.cc
+++ b/flang/lib/evaluate/expression.cc
@@ -189,6 +189,16 @@ template<typename T> DynamicType ArrayConstructor<T>::GetType() const {
   return result.GetType();
 }
 
+template<typename A>
+typename ExpressionBase<A>::Derived &ExpressionBase<A>::derived() {
+  return *static_cast<Derived *>(this);
+}
+
+template<typename A>
+const typename ExpressionBase<A>::Derived &ExpressionBase<A>::derived() const {
+  return *static_cast<const Derived *>(this);
+}
+
 template<typename A>
 std::optional<DynamicType> ExpressionBase<A>::GetType() const {
   if constexpr (IsLengthlessIntrinsicType<Result>) {
diff --git a/flang/lib/evaluate/expression.h b/flang/lib/evaluate/expression.h
index c2300071fbd2..832a6baa3717 100644
--- a/flang/lib/evaluate/expression.h
+++ b/flang/lib/evaluate/expression.h
@@ -68,8 +68,8 @@ public:
 
 private:
   using Derived = Expr<Result>;
-  Derived &derived() { return *static_cast<Derived *>(this); }
-  const Derived &derived() const { return *static_cast<const Derived *>(this); }
+  Derived &derived();
+  const Derived &derived() const;
 
 public:
   template<typename A> Derived &operator=(const A &x) {