diff --git a/lang/nodes/include/basic_nodes.hpp b/lang/nodes/include/basic_nodes.hpp
index d816249..ecc0a07 100644
--- a/lang/nodes/include/basic_nodes.hpp
+++ b/lang/nodes/include/basic_nodes.hpp
@@ -146,8 +146,15 @@ inline bool can_cast_modifier(Modifier from, Modifier to) {
     break;
   }
 
-  error_handling::handle_general_error("Unreachable");
-  exit(1); // unreachable
+  ::utils::Assert(false, "uUnreachable");
+  ::utils::unreachable();
+}
+
+inline std::optional<Modifier> choose_min_modifier(Modifier /*left*/,
+                                                   Modifier /*right*/) {
+  // TODO: FIXME: implement
+  ::utils::Assert(false, "choose_min_modifier is not implemented yet");
+  return {};
 }
 
 } // namespace utils
diff --git a/lang/nodes/src/type_nodes.cpp b/lang/nodes/src/type_nodes.cpp
index b0ff2af..425a4f8 100644
--- a/lang/nodes/src/type_nodes.cpp
+++ b/lang/nodes/src/type_nodes.cpp
@@ -233,12 +233,20 @@ bool TypeStorage::Unify(Type left_id, Type right_id, UnifyModePolicy policy) {
   switch (policy) {
   case UnifyModePolicy::kIgnore:
     break;
-  case UnifyModePolicy::kApplyStrongest:
-    left.modifier = utils::ChooseMinModifier(left.modifier, right.modifier);
-    right.modifier = left.modifier;
+  case UnifyModePolicy::kApplyStrongest: {
+    const auto min_modifier =
+        utils::choose_min_modifier(left.modifier, right.modifier);
+
+    if (not min_modifier.has_value()) {
+      return false;
+    }
+
+    left.modifier = min_modifier.value();
+    right.modifier = min_modifier.value();
     break;
+  }
   case UnifyModePolicy::kCheckLeftIsSubmode:
-    if (not utils::IsSubmodifier(left.modifier, right.modifier)) {
+    if (not utils::can_cast_modifier(left.modifier, right.modifier)) {
       return false;
     }
     break;
@@ -314,6 +322,8 @@ bool TypeStorage::Resolve(Type generic, const TypeData &replacement,
       type.modifier = modifier;
     }
   }
+
+  return true;
 }
 
 //