diff --git a/include/serene/exprs/def.h b/include/serene/exprs/def.h
index 25e64cb..45c34c2 100644
--- a/include/serene/exprs/def.h
+++ b/include/serene/exprs/def.h
@@ -55,8 +55,12 @@ public:
   static bool classof(const Expression *e);
 
   /// Create a Def node out a list. The list should contain the
-  /// correct `def` form like `(def blah value)`.
-  static maybe_node make(List *);
+  /// correct `def` form like `(def blah value)`. This function
+  /// is supposed to be used in the semantic analysis phase.
+  ///
+  /// \param ctx The semantic analysis context object.
+  /// \param list the list containing the `def` form
+  static maybe_node make(reader::SemanticContext &ctx, List *list);
   ~Def() = default;
 };
 
diff --git a/include/serene/exprs/fn.h b/include/serene/exprs/fn.h
index 5c2cf8e..05c8572 100644
--- a/include/serene/exprs/fn.h
+++ b/include/serene/exprs/fn.h
@@ -60,8 +60,13 @@ public:
 
   /// Creates a function node out of a function definition
   /// in a list. the list has to contain the correct definition
-  /// of a function, for exmaple: `(fn (args1 arg2) body)`
-  static maybe_node make(List *);
+  /// of a function, for exmaple: `(fn (args1 arg2) body)`.This function
+  /// is supposed to be used in the semantic analysis phase.
+  ///
+  /// \param ctx The semantic analysis context object.
+  /// \param list the list containing the `fn` form
+  static maybe_node make(reader::SemanticContext &ctx, List *list);
+
   ~Fn() = default;
 };
 
diff --git a/src/serene/exprs/def.cpp b/src/serene/exprs/def.cpp
index dfed383..03016fb 100644
--- a/src/serene/exprs/def.cpp
+++ b/src/serene/exprs/def.cpp
@@ -46,26 +46,48 @@ bool Def::classof(const Expression *e) {
   return e->getType() == ExprType::Def;
 };
 
-maybe_node Def::make(List *list) {
+maybe_node Def::make(reader::SemanticContext &ctx, List *list) {
   // TODO: Add support for docstring as the 3rd argument (4th element)
+
   if (list->count() != 3) {
     std::string msg = llvm::formatv("Expected 3 got {0}", list->count());
     return Result<node>::success(makeAndCast<errors::Error>(
         &errors::DefWrongNumberOfArgs, list->elements[0], msg));
   }
 
+  // Make sure that the list starts with a `def`
   Symbol *defSym = llvm::dyn_cast<Symbol>(list->elements[0].get());
   assert((defSym && defSym->name == "def") &&
          "The first element of the list should be a 'def'.");
 
+  // Make sure that the first argument is a Symbol
   Symbol *binding = llvm::dyn_cast<Symbol>(list->elements[1].get());
-
   if (!binding) {
     return Result<node>::success(makeAndCast<errors::Error>(
         &errors::DefExpectSymbol, list->elements[1], ""));
   }
 
-  node def = exprs::make<Def>(list->location, binding->name, list->elements[2]);
+  // Analyze the value
+  maybe_node value = list->elements[2]->analyze(ctx);
+  node analyzedValue;
+
+  if (value) {
+    // Success value
+    auto &valueNode = value.getValue();
+
+    if (valueNode) {
+      // A rewrite is necessary
+      analyzedValue = valueNode;
+    } else {
+      // no rewrite
+      analyzedValue = list->elements[2];
+    }
+  } else {
+    // Error value
+    return value;
+  }
+
+  node def = exprs::make<Def>(list->location, binding->name, analyzedValue);
   return Result<node>::success(def);
 };
 } // namespace exprs
diff --git a/src/serene/exprs/fn.cpp b/src/serene/exprs/fn.cpp
index 41d969e..336ff90 100644
--- a/src/serene/exprs/fn.cpp
+++ b/src/serene/exprs/fn.cpp
@@ -47,7 +47,7 @@ maybe_node Fn::analyze(reader::SemanticContext &ctx) {
 
 bool Fn::classof(const Expression *e) { return e->getType() == ExprType::Fn; };
 
-maybe_node Fn::make(List *list) {
+maybe_node Fn::make(reader::SemanticContext &ctx, List *list) {
   // TODO: Add support for docstring as the 3rd argument (4th element)
   if (list->count() < 2) {
     std::string msg =
diff --git a/src/serene/exprs/list.cpp b/src/serene/exprs/list.cpp
index 8bb1369..984bcff 100644
--- a/src/serene/exprs/list.cpp
+++ b/src/serene/exprs/list.cpp
@@ -64,11 +64,11 @@ maybe_node List::analyze(reader::SemanticContext &ctx) {
 
       if (sym) {
         if (sym->name == "def") {
-          return Def::make(this);
+          return Def::make(ctx, this);
         }
 
         if (sym->name == "fn") {
-          return Fn::make(this);
+          return Fn::make(ctx, this);
         }
       }
 
diff --git a/src/tests/exprs/list_tests.cpp.inc b/src/tests/exprs/list_tests.cpp.inc
index fc693fa..788a7dd 100644
--- a/src/tests/exprs/list_tests.cpp.inc
+++ b/src/tests/exprs/list_tests.cpp.inc
@@ -100,6 +100,12 @@ TEST_CASE("List semantic analysis of 'def'", "[semantic]") {
   afterAst = analyzer.analyze(ast.getValue());
   REQUIRE(afterAst);
   CHECK(astToString(&afterAst.getValue()) == "<Def a -> <Symbol b>>");
+
+  ast = reader::read("(def a (fn () a))");
+  afterAst = analyzer.analyze(ast.getValue());
+  REQUIRE(afterAst);
+  CHECK(astToString(&afterAst.getValue()) ==
+        "<Def a -> <Fn Anonymous <List -> to <Symbol a>>>");
 }
 
 TEST_CASE("List semantic analysis for 'fn'", "[semantic]") {
@@ -107,22 +113,25 @@ TEST_CASE("List semantic analysis for 'fn'", "[semantic]") {
   auto ast = reader::read("(fn)");
   auto afterAst = analyzer.analyze(ast.getValue());
   REQUIRE(afterAst);
-  CHECK(astToString(&afterAst.getValue()) == "<Error E3: The argument list is mandatory.>");
+  CHECK(astToString(&afterAst.getValue()) ==
+        "<Error E3: The argument list is mandatory.>");
 
   ast = reader::read("(fn ())");
   afterAst = analyzer.analyze(ast.getValue());
   REQUIRE(afterAst);
-  CHECK(astToString(&afterAst.getValue()) ==  "<Fn Anonymous <List -> to <>>");
+  CHECK(astToString(&afterAst.getValue()) == "<Fn Anonymous <List -> to <>>");
 
   ast = reader::read("(fn (a b c) a a a)");
   afterAst = analyzer.analyze(ast.getValue());
   REQUIRE(afterAst);
-  CHECK(astToString(&afterAst.getValue()) ==  "<Fn Anonymous <List -> to <Symbol a> <Symbol a> <Symbol a>>");
+  CHECK(astToString(&afterAst.getValue()) ==
+        "<Fn Anonymous <List -> to <Symbol a> <Symbol a> <Symbol a>>");
 
   ast = reader::read("(fn () a b)");
   afterAst = analyzer.analyze(ast.getValue());
   REQUIRE(afterAst);
-  CHECK(astToString(&afterAst.getValue()) == "<Fn Anonymous <List -> to <Symbol a> <Symbol b>>");
+  CHECK(astToString(&afterAst.getValue()) ==
+        "<Fn Anonymous <List -> to <Symbol a> <Symbol b>>");
 }
 } // namespace exprs
 } // namespace serene