diff --git a/mypy/nodes.py b/mypy/nodes.py
index 56c61ce26d63..9e26103e2f58 100644
--- a/mypy/nodes.py
+++ b/mypy/nodes.py
@@ -1263,7 +1263,7 @@ class Block(Statement):
 
     __match_args__ = ("body", "is_unreachable")
 
-    def __init__(self, body: list[Statement]) -> None:
+    def __init__(self, body: list[Statement], *, is_unreachable: bool = False) -> None:
         super().__init__()
         self.body = body
         # True if we can determine that this block is not executed during semantic
@@ -1271,7 +1271,7 @@ def __init__(self, body: list[Statement]) -> None:
         # something like "if PY3:" when using Python 2. However, some code is
         # only considered unreachable during type checking and this is not true
         # in those cases.
-        self.is_unreachable = False
+        self.is_unreachable = is_unreachable
 
     def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_block(self)
diff --git a/mypy/treetransform.py b/mypy/treetransform.py
index bb34d8de2884..aafa4e95d530 100644
--- a/mypy/treetransform.py
+++ b/mypy/treetransform.py
@@ -276,7 +276,7 @@ def visit_nonlocal_decl(self, node: NonlocalDecl) -> NonlocalDecl:
         return NonlocalDecl(node.names.copy())
 
     def visit_block(self, node: Block) -> Block:
-        return Block(self.statements(node.body))
+        return Block(self.statements(node.body), is_unreachable=node.is_unreachable)
 
     def visit_decorator(self, node: Decorator) -> Decorator:
         # Note that a Decorator must be transformed to a Decorator.
diff --git a/test-data/unit/check-unreachable-code.test b/test-data/unit/check-unreachable-code.test
index cbad1bd5449e..e6818ab5c3c7 100644
--- a/test-data/unit/check-unreachable-code.test
+++ b/test-data/unit/check-unreachable-code.test
@@ -1000,6 +1000,16 @@ class Test4(Generic[T3]):
 
 [builtins fixtures/isinstancelist.pyi]
 
+[case testUnreachableBlockStaysUnreachableWithTypeVarConstraints]
+# flags: --always-false COMPILE_TIME_FALSE
+from typing import TypeVar
+COMPILE_TIME_FALSE = False
+T = TypeVar("T", int, str)
+def foo(x: T) -> T:
+    if COMPILE_TIME_FALSE:
+        return "bad"
+    return x
+
 [case testUnreachableFlagContextManagersNoSuppress]
 # flags: --warn-unreachable
 from contextlib import contextmanager