diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6009ae5cb..9b6f55ff9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Rejection of invalid parameter types and return types in function declarations (eng/recordflux/RecordFlux#977)
+- Consequential errors caused by undefined variables in binary expressions (eng/recordflux/RecordFlux#1672)
 
 ## [0.24.0] - 2024-09-12
 
diff --git a/rflx/expr.py b/rflx/expr.py
index 9d0cadb7a..b3ad6de2c 100644
--- a/rflx/expr.py
+++ b/rflx/expr.py
@@ -823,7 +823,8 @@ def _check_type_subexpr(self) -> RecordFluxError:
         for e in [self.left, self.right]:
             error.extend(e.check_type_instance(ty.AnyInteger).entries)
 
-        self.type_ = ty.common_type([self.left.type_, self.right.type_])
+        common_type = ty.common_type([self.left.type_, self.right.type_])
+        self.type_ = common_type if common_type != ty.UNDEFINED else ty.BASE_INTEGER
 
         return error
 
diff --git a/tests/unit/model/message_test.py b/tests/unit/model/message_test.py
index 36b83c94a..3f9ab85ef 100644
--- a/tests/unit/model/message_test.py
+++ b/tests/unit/model/message_test.py
@@ -1067,7 +1067,22 @@ def test_reference_to_optional_field_1() -> None:
     )
 
 
-def test_reference_to_optional_field_2() -> None:
+@pytest.mark.parametrize(
+    ("size_expression"),
+    [
+        Mul(
+            Variable("Opt", location=Location((10, 30))),
+            Number(8),
+            location=Location((10, 20)),
+        ),
+        Sub(
+            Variable("Opt", location=Location((10, 30))),
+            Number(8),
+            location=Location((10, 20)),
+        ),
+    ],
+)
+def test_reference_to_optional_field_2(size_expression: Expr) -> None:
     structure = [
         Link(INITIAL, Field(ID("Flag", location=Location((1, 1))))),
         Link(
@@ -1087,11 +1102,7 @@ def test_reference_to_optional_field_2() -> None:
         Link(
             Field(ID("Any", location=Location((5, 5)))),
             Field(ID("Data", location=Location((5, 6)))),
-            size=Mul(
-                Variable("Opt", location=Location((10, 30))),
-                Number(8),
-                location=Location((10, 20)),
-            ),
+            size=size_expression,
         ),
         Link(Field(ID("Data", location=Location((7, 7)))), FINAL),
     ]