diff --git a/include/CMakeLists.txt b/include/CMakeLists.txt
index b41736c7..e4c61dfb 100644
--- a/include/CMakeLists.txt
+++ b/include/CMakeLists.txt
@@ -8,6 +8,7 @@ set(Oasis_HEADERS
     Oasis/EulerNumber.hpp
     Oasis/Exponent.hpp
     Oasis/Expression.hpp
+    Oasis/FwdDecls.hpp
     Oasis/Imaginary.hpp
     Oasis/Integral.hpp
     Oasis/LeafExpression.hpp
diff --git a/include/Oasis/Concepts.hpp b/include/Oasis/Concepts.hpp
index 94500df4..428df464 100644
--- a/include/Oasis/Concepts.hpp
+++ b/include/Oasis/Concepts.hpp
@@ -5,6 +5,8 @@
 #ifndef OASIS_CONCEPTS_HPP
 #define OASIS_CONCEPTS_HPP
 
+#include <expected>
+
 namespace Oasis {
 
 class Expression;
diff --git a/include/Oasis/FwdDecls.hpp b/include/Oasis/FwdDecls.hpp
new file mode 100644
index 00000000..38a443e7
--- /dev/null
+++ b/include/Oasis/FwdDecls.hpp
@@ -0,0 +1,50 @@
+//
+// Created by Matthew McCall on 12/9/25.
+//
+
+#ifndef OASIS_FWDDECLS_HPP
+#define OASIS_FWDDECLS_HPP
+
+#include "Concepts.hpp"
+
+namespace Oasis {
+class Real;
+class Imaginary;
+class Matrix;
+class Variable;
+class Undefined;
+class EulerNumber;
+class Pi;
+
+template <IExpression, IExpression>
+class Add;
+
+template <IExpression MinuendT, IExpression SubtrahendT>
+class Subtract;
+
+template <IExpression MultiplicandT, IExpression MultiplierT>
+class Multiply;
+
+template <IExpression DividendT, IExpression DivisorT>
+class Divide;
+
+template <IExpression BaseT, IExpression PowerT>
+class Exponent;
+
+template <IExpression BaseT, IExpression ArgumentT>
+class Log;
+
+template <typename OperandT>
+class Negate;
+
+template <typename OperandT>
+class Magnitude;
+
+template <IExpression, IExpression>
+class Derivative;
+
+template <IExpression Integrand, IExpression Differential>
+class Integral;
+}
+
+#endif // OASIS_FWDDECLS_HPP
diff --git a/include/Oasis/Visit.hpp b/include/Oasis/Visit.hpp
index 12fa687d..408ee544 100644
--- a/include/Oasis/Visit.hpp
+++ b/include/Oasis/Visit.hpp
@@ -5,48 +5,11 @@
 #ifndef OASIS_SERIALIZATION_HPP
 #define OASIS_SERIALIZATION_HPP
 
+#include "FwdDecls.hpp"
 #include "Expression.hpp"
 
 namespace Oasis {
 
-class Real;
-class Imaginary;
-class Matrix;
-class Variable;
-class Undefined;
-class EulerNumber;
-class Pi;
-
-template <IExpression, IExpression>
-class Add;
-
-template <IExpression MinuendT, IExpression SubtrahendT>
-class Subtract;
-
-template <IExpression MultiplicandT, IExpression MultiplierT>
-class Multiply;
-
-template <IExpression DividendT, IExpression DivisorT>
-class Divide;
-
-template <IExpression BaseT, IExpression PowerT>
-class Exponent;
-
-template <IExpression BaseT, IExpression ArgumentT>
-class Log;
-
-template <typename OperandT>
-class Negate;
-
-template <typename OperandT>
-class Magnitude;
-
-template <IExpression, IExpression>
-class Derivative;
-
-template <IExpression Integrand, IExpression Differential>
-class Integral;
-
 class Visitor {
 public:
     virtual any Visit(const Real& real) = 0;