diff --git a/compile.c b/compile.c
index 3f25f5f..dcb180a 100644
--- a/compile.c
+++ b/compile.c
@@ -56,6 +56,11 @@ static bool promote(env_t *env, CORD *code, type_t *actual, type_t *needed)
         return true;
     }
 
+    if (needed->tag == FunctionType && actual->tag == FunctionType) {
+        *code = CORD_all("(", compile_type(env, needed), ")", *code);
+        return true;
+    }
+
     return false;
 }
 
@@ -1710,7 +1715,10 @@ CORD compile(env_t *env, ast_t *ast)
                     binding_t *b = get_namespace_binding(env, impl, field->name);
                     if (b) {
                         // TODO: typecheck implementation!
-                        c = CORD_all(c, ", (void*)", b->code);
+                        CORD field_code = b->code;
+                        if (!promote(env, &field_code, b->type, field->type))
+                            code_err(ast, "I can't promote the method '%s' from %T to %T", field->name, b->type, field->type);
+                        c = CORD_all(c, ", ", field_code);
                     } else {
                         type_t *member_t = get_field_type(impl_t, field->name);
                         if (!member_t)
diff --git a/types.c b/types.c
index 85060b4..ca0f77f 100644
--- a/types.c
+++ b/types.c
@@ -270,6 +270,19 @@ bool can_promote(type_t *actual, type_t *needed)
     if (needed->tag == ClosureType && actual->tag == FunctionType)
         return type_eq(actual, Match(needed, ClosureType)->fn);
 
+    if (actual->tag == FunctionType && needed->tag == FunctionType) {
+        for (arg_t *actual_arg = Match(actual, FunctionType)->args, *needed_arg = Match(needed, FunctionType)->args;
+             actual_arg || needed_arg; actual_arg = actual_arg->next, needed_arg = needed_arg->next) {
+            if (!actual_arg || !needed_arg) return false;
+            if (type_eq(actual_arg->type, needed_arg->type)) continue;
+            if (actual_arg->type->tag == PointerType && needed_arg->type->tag == PointerType
+                && can_promote(actual_arg->type, needed_arg->type))
+                continue;
+            return false;
+        }
+        return true;
+    }
+
     return false;
 }