diff --git a/test-data/unit/check-enum.test b/test-data/unit/check-enum.test
index c05dfdef2bf7..51d982f35a44 100644
--- a/test-data/unit/check-enum.test
+++ b/test-data/unit/check-enum.test
@@ -866,6 +866,7 @@ main:2: note: Revealed type is "Literal[1]?"
 main:2: note: Revealed type is "Literal['foo']?"
 
 [case testEnumReachabilityChecksBasic]
+# flags: --warn-unreachable
 from enum import Enum
 from typing import Literal
 
@@ -882,7 +883,7 @@ elif x is Foo.B:
 elif x is Foo.C:
     reveal_type(x)  # N: Revealed type is "Literal[__main__.Foo.C]"
 else:
-    reveal_type(x)  # No output here: this branch is unreachable
+    reveal_type(x)  # E: Statement is unreachable
 reveal_type(x) # N: Revealed type is "Literal[__main__.Foo.A] | Literal[__main__.Foo.B] | Literal[__main__.Foo.C]"
 
 if Foo.A is x:
@@ -892,7 +893,7 @@ elif Foo.B is x:
 elif Foo.C is x:
     reveal_type(x)  # N: Revealed type is "Literal[__main__.Foo.C]"
 else:
-    reveal_type(x)  # No output here: this branch is unreachable
+    reveal_type(x)  # E: Statement is unreachable
 reveal_type(x) # N: Revealed type is "Literal[__main__.Foo.A] | Literal[__main__.Foo.B] | Literal[__main__.Foo.C]"
 
 y: Foo
@@ -903,7 +904,7 @@ elif y is Foo.B:
 elif y is Foo.C:
     reveal_type(y)  # N: Revealed type is "Literal[__main__.Foo.C]"
 else:
-    reveal_type(y)  # No output here: this branch is unreachable
+    reveal_type(y)  # E: Statement is unreachable
 reveal_type(y) # N: Revealed type is "__main__.Foo"
 
 if Foo.A is y:
@@ -913,11 +914,12 @@ elif Foo.B is y:
 elif Foo.C is y:
     reveal_type(y)  # N: Revealed type is "Literal[__main__.Foo.C]"
 else:
-    reveal_type(y)  # No output here: this branch is unreachable
+    reveal_type(y)  # E: Statement is unreachable
 reveal_type(y) # N: Revealed type is "__main__.Foo"
 [builtins fixtures/bool.pyi]
 
 [case testEnumReachabilityChecksWithOrdering]
+# flags: --warn-unreachable
 from enum import Enum
 from typing import Literal
 
@@ -934,7 +936,7 @@ if x is Foo.A:
 elif x is Foo.B:
     reveal_type(x)  # N: Revealed type is "Literal[__main__.Foo.B]"
 else:
-    reveal_type(x)  # No output here: this branch is unreachable
+    reveal_type(x)  # E: Statement is unreachable
 
 class Bar(Enum):
     __order__ = "A B"
@@ -949,7 +951,7 @@ if y is Bar.A:
 elif y is Bar.B:
     reveal_type(y)  # N: Revealed type is "Literal[__main__.Bar.B]"
 else:
-    reveal_type(y)  # No output here: this branch is unreachable
+    reveal_type(y)  # E: Statement is unreachable
 
 x2: Foo
 if x2 is Foo.A:
@@ -957,7 +959,7 @@ if x2 is Foo.A:
 elif x2 is Foo.B:
     reveal_type(x2)  # N: Revealed type is "Literal[__main__.Foo.B]"
 else:
-    reveal_type(x2)  # No output here: this branch is unreachable
+    reveal_type(x2)  # E: Statement is unreachable
 
 y2: Bar
 if y2 is Bar.A:
@@ -965,10 +967,11 @@ if y2 is Bar.A:
 elif y2 is Bar.B:
     reveal_type(y2)  # N: Revealed type is "Literal[__main__.Bar.B]"
 else:
-    reveal_type(y2)  # No output here: this branch is unreachable
+    reveal_type(y2)  # E: Statement is unreachable
 [builtins fixtures/tuple.pyi]
 
 [case testEnumReachabilityChecksIndirect]
+# flags: --warn-unreachable
 from enum import Enum
 from typing import Final, Literal
 
@@ -1022,18 +1025,19 @@ if y is z:
     reveal_type(z)  # N: Revealed type is "Literal[__main__.Foo.A]?"
     accepts_foo_a(z)
 else:
-    reveal_type(y)  # No output: this branch is unreachable
-    reveal_type(z)  # No output: this branch is unreachable
+    reveal_type(y)  # E: Statement is unreachable
+    reveal_type(z)
 if z is y:
     reveal_type(y)  # N: Revealed type is "Literal[__main__.Foo.A]"
     reveal_type(z)  # N: Revealed type is "Literal[__main__.Foo.A]?"
     accepts_foo_a(z)
 else:
-    reveal_type(y)  # No output: this branch is unreachable
-    reveal_type(z)  # No output: this branch is unreachable
+    reveal_type(y)  # E: Statement is unreachable
+    reveal_type(z)
 [builtins fixtures/bool.pyi]
 
 [case testEnumReachabilityNarrowingForUnionMessiness]
+# flags: --warn-unreachable
 from enum import Enum
 from typing import Literal
 
@@ -1062,6 +1066,7 @@ else:
 [builtins fixtures/bool.pyi]
 
 [case testEnumReachabilityWithNone]
+# flags: --warn-unreachable
 from enum import Enum
 from typing import Optional
 
@@ -1089,6 +1094,7 @@ reveal_type(x) # N: Revealed type is "__main__.Foo | None"
 [builtins fixtures/enum.pyi]
 
 [case testEnumReachabilityWithMultipleEnums]
+# flags: --warn-unreachable
 from enum import Enum
 from typing import Literal, Union
 
@@ -1123,6 +1129,7 @@ reveal_type(x3) # N: Revealed type is "__main__.Foo | __main__.Bar"
 [builtins fixtures/bool.pyi]
 
 [case testEnumReachabilityPEP484ExampleWithFinal]
+# flags: --warn-unreachable
 from typing import Final, Union
 from enum import Enum
 
@@ -1146,6 +1153,7 @@ def func(x: Union[int, None, Empty] = _empty) -> int:
 [builtins fixtures/primitives.pyi]
 
 [case testEnumReachabilityPEP484ExampleWithMultipleValues]
+# flags: --warn-unreachable
 from typing import Union
 from enum import Enum
 
@@ -1168,6 +1176,7 @@ def process(response: Union[str, Reason] = '') -> str:
 
 
 [case testEnumReachabilityPEP484ExampleSingleton]
+# flags: --warn-unreachable
 from typing import Final, Union
 from enum import Enum
 
@@ -1191,7 +1200,7 @@ def func(x: Union[int, None, Empty] = _empty) -> int:
 [builtins fixtures/primitives.pyi]
 
 [case testEnumReachabilityPEP484ExampleSingletonWithMethod]
-# flags: --python-version 3.11
+# flags: --python-version 3.11 --warn-unreachable
 from typing import Final, Union
 from enum import Enum, member
 
@@ -1232,6 +1241,7 @@ reveal_type(A().b)  # N: Revealed type is "Any"
 [builtins fixtures/enum.pyi]
 
 [case testEnumReachabilityWithChaining]
+# flags: --warn-unreachable
 from enum import Enum
 
 class Foo(Enum):
diff --git a/test-data/unit/check-functions.test b/test-data/unit/check-functions.test
index 542cbb3fd22c..699e83ccbd9f 100644
--- a/test-data/unit/check-functions.test
+++ b/test-data/unit/check-functions.test
@@ -1523,15 +1523,16 @@ else:
                     # N:     def f(int, /) -> None
 
 [case testConditionalFunctionDefinitionUnreachable]
+# flags: --warn-unreachable
 def bar() -> None:
     if False:
-        foo = 1
+        foo = 1  # E: Statement is unreachable
     else:
         def foo(obj): ...
 
 def baz() -> None:
     if False:
-        foo: int = 1
+        foo: int = 1  # E: Statement is unreachable
     else:
         def foo(obj): ...  # E: Incompatible redefinition (redefinition with type "Callable[[Any], Any]", original type "int")
 [builtins fixtures/tuple.pyi]
diff --git a/test-data/unit/check-protocols.test b/test-data/unit/check-protocols.test
index 447989082088..a51445ef0b5b 100644
--- a/test-data/unit/check-protocols.test
+++ b/test-data/unit/check-protocols.test
@@ -1729,6 +1729,7 @@ if isinstance(x, Iterable):
 [typing fixtures/typing-full.pyi]
 
 [case testConcreteClassesInProtocolsIsInstance]
+# flags: --warn-unreachable
 from typing import Protocol, runtime_checkable, TypeVar, Generic
 
 T = TypeVar('T')
@@ -1757,25 +1758,25 @@ c = C()
 if isinstance(c, P1):
     reveal_type(c) # N: Revealed type is "__main__.C"
 else:
-    reveal_type(c) # Unreachable
+    reveal_type(c)  # E: Statement is unreachable
 if isinstance(c, P):
     reveal_type(c) # N: Revealed type is "__main__.C"
 else:
-    reveal_type(c) # Unreachable
+    reveal_type(c)  # E: Statement is unreachable
 
 c1i: C1[int]
 if isinstance(c1i, P1):
     reveal_type(c1i) # N: Revealed type is "__main__.C1[builtins.int]"
 else:
-    reveal_type(c1i) # Unreachable
+    reveal_type(c1i)  # E: Statement is unreachable
 if isinstance(c1i, P):
     reveal_type(c1i) # N: Revealed type is "__main__.<subclass of "__main__.C1[builtins.int]" and "__main__.P">"
 else:
     reveal_type(c1i) # N: Revealed type is "__main__.C1[builtins.int]"
 
 c1s: C1[str]
-if isinstance(c1s, P1):
-    reveal_type(c1s) # Unreachable
+if isinstance(c1s, P1):  # E: Subclass of "C1[str]" and "P1" cannot exist: would have incompatible method signatures
+    reveal_type(c1s)  # E: Statement is unreachable
 else:
     reveal_type(c1s) # N: Revealed type is "__main__.C1[builtins.str]"