diff --git a/crates/red_knot_python_semantic/src/types/infer.rs b/crates/red_knot_python_semantic/src/types/infer.rs
index a00f9d4e8b..42b4297dfd 100644
--- a/crates/red_knot_python_semantic/src/types/infer.rs
+++ b/crates/red_knot_python_semantic/src/types/infer.rs
@@ -4568,10 +4568,14 @@ impl<'db> TypeInferenceBuilder<'db> {
                 UnionType::from_elements(self.db, [param_type, Type::none(self.db)])
             }
             KnownInstanceType::Union => match parameters {
-                ast::Expr::Tuple(t) => UnionType::from_elements(
-                    self.db,
-                    t.iter().map(|elt| self.infer_type_expression(elt)),
-                ),
+                ast::Expr::Tuple(t) => {
+                    let union_ty = UnionType::from_elements(
+                        self.db,
+                        t.iter().map(|elt| self.infer_type_expression(elt)),
+                    );
+                    self.store_expression_type(parameters, union_ty);
+                    union_ty
+                }
                 _ => self.infer_type_expression(parameters),
             },
             KnownInstanceType::TypeVar(_) => todo_type!(),
diff --git a/crates/red_knot_workspace/resources/test/corpus/95_annotation_union.py b/crates/red_knot_workspace/resources/test/corpus/95_annotation_union.py
new file mode 100644
index 0000000000..79be74b631
--- /dev/null
+++ b/crates/red_knot_workspace/resources/test/corpus/95_annotation_union.py
@@ -0,0 +1,3 @@
+from typing import Union
+
+x: Union[int, str] = 1