diff --git a/code/compiler/06/ast.hpp b/code/compiler/06/ast.hpp
index 3f35db3..21e1f61 100644
--- a/code/compiler/06/ast.hpp
+++ b/code/compiler/06/ast.hpp
@@ -58,7 +58,7 @@ struct definition {
     
     virtual void typecheck_first(type_mgr& mgr, type_env& env) = 0;
     virtual void typecheck_second(type_mgr& mgr, const type_env& env) const = 0;
-    virtual void resolve(const type_mgr& mgr) const = 0;
+    virtual void resolve(const type_mgr& mgr) = 0;
 };
 
 using definition_ptr = std::unique_ptr<definition>;
@@ -175,7 +175,7 @@ struct definition_defn : public definition {
 
     void typecheck_first(type_mgr& mgr, type_env& env);
     void typecheck_second(type_mgr& mgr, const type_env& env) const;
-    void resolve(const type_mgr& mgr) const;
+    void resolve(const type_mgr& mgr);
 };
 
 struct definition_data : public definition {
@@ -187,5 +187,5 @@ struct definition_data : public definition {
 
     void typecheck_first(type_mgr& mgr, type_env& env);
     void typecheck_second(type_mgr& mgr, const type_env& env) const;
-    void resolve(const type_mgr& mgr) const;
+    void resolve(const type_mgr& mgr);
 };
diff --git a/code/compiler/06/definition.cpp b/code/compiler/06/definition.cpp
index ff1ef23..5047055 100644
--- a/code/compiler/06/definition.cpp
+++ b/code/compiler/06/definition.cpp
@@ -1,4 +1,5 @@
 #include "ast.hpp"
+#include "error.hpp"
 
 void definition_defn::typecheck_first(type_mgr& mgr, type_env& env) {
     return_type = mgr.new_type();
@@ -28,8 +29,16 @@ void definition_defn::typecheck_second(type_mgr& mgr, const type_env& env) const
     mgr.unify(return_type, body_type);
 }
 
-void definition_defn::resolve(const type_mgr& mgr) const {
+void definition_defn::resolve(const type_mgr& mgr) {
+    type_var* var;
     body->resolve_common(mgr);
+
+    return_type = mgr.resolve(return_type, var);
+    if(var) throw type_error("ambiguously typed program");
+    for(auto& param_type : param_types) {
+        param_type = mgr.resolve(param_type, var);
+        if(var) throw type_error("ambiguously typed program");
+    }
 }
 
 void definition_data::typecheck_first(type_mgr& mgr, type_env& env) {
@@ -54,7 +63,7 @@ void definition_data::typecheck_second(type_mgr& mgr, const type_env& env) const
     // Nothing
 }
 
-void definition_data::resolve(const type_mgr& mgr) const {
+void definition_data::resolve(const type_mgr& mgr) {
     // Nothing
 }