diff --git a/mypy/build.py b/mypy/build.py
index 7913eae9c6ed..d48d95062fcc 100644
--- a/mypy/build.py
+++ b/mypy/build.py
@@ -2239,7 +2239,6 @@ def semantic_analysis_pass1(self) -> None:
         analyzer = SemanticAnalyzerPreAnalysis()
         with self.wrap_context():
             analyzer.visit_file(self.tree, self.xpath, self.id, options)
-        self.manager.errors.set_unreachable_lines(self.xpath, self.tree.unreachable_lines)
         # TODO: Do this while constructing the AST?
         self.tree.names = SymbolTable()
         if not self.tree.is_stub:
diff --git a/mypy/errors.py b/mypy/errors.py
index 9d29259e943c..91a9509591c1 100644
--- a/mypy/errors.py
+++ b/mypy/errors.py
@@ -222,9 +222,6 @@ class Errors:
     # (path -> line -> error-codes)
     ignored_lines: dict[str, dict[int, list[str]]]
 
-    # Lines that are statically unreachable (e.g. due to platform/version check).
-    unreachable_lines: dict[str, set[int]]
-
     # Lines on which an error was actually ignored.
     used_ignored_lines: dict[str, dict[int, list[str]]]
 
@@ -280,7 +277,6 @@ def initialize(self) -> None:
         self.import_ctx = []
         self.function_or_member = [None]
         self.ignored_lines = {}
-        self.unreachable_lines = {}
         self.used_ignored_lines = defaultdict(lambda: defaultdict(list))
         self.ignored_files = set()
         self.only_once_messages = set()
@@ -329,9 +325,6 @@ def set_file_ignored_lines(
         if ignore_all:
             self.ignored_files.add(file)
 
-    def set_unreachable_lines(self, file: str, unreachable_lines: set[int]) -> None:
-        self.unreachable_lines[file] = unreachable_lines
-
     def current_target(self) -> str | None:
         """Retrieves the current target from the associated scope.
 
@@ -630,8 +623,6 @@ def generate_unused_ignore_errors(self, file: str) -> None:
         ignored_lines = self.ignored_lines[file]
         used_ignored_lines = self.used_ignored_lines[file]
         for line, ignored_codes in ignored_lines.items():
-            if line in self.unreachable_lines[file]:
-                continue
             if codes.UNUSED_IGNORE.code in ignored_codes:
                 continue
             used_ignored_codes = used_ignored_lines[line]
diff --git a/mypy/nodes.py b/mypy/nodes.py
index 8457e39b6aa1..f7d9f799c533 100644
--- a/mypy/nodes.py
+++ b/mypy/nodes.py
@@ -11,6 +11,7 @@
     Any,
     Callable,
     Dict,
+    Iterable,
     Iterator,
     List,
     Optional,
@@ -314,8 +315,6 @@ class MypyFile(SymbolNode):
     # If the value is empty, ignore all errors; otherwise, the list contains all
     # error codes to ignore.
     ignored_lines: dict[int, list[str]]
-    # Lines that are statically unreachable (e.g. due to platform/version check).
-    unreachable_lines: set[int]
     # Is this file represented by a stub file (.pyi)?
     is_stub: bool
     # Is this loaded from the cache and thus missing the actual body of the file?
@@ -348,7 +347,6 @@ def __init__(
             self.ignored_lines = ignored_lines
         else:
             self.ignored_lines = {}
-        self.unreachable_lines = set()
 
         self.path = ""
         self.is_stub = False
@@ -380,6 +378,11 @@ def is_package_init_file(self) -> bool:
     def is_future_flag_set(self, flag: str) -> bool:
         return flag in self.future_import_flags
 
+    def remove_ignored_lines(self, lines: Iterable[int]) -> None:
+        """Called to prevent spurious 'unused-ignore' errors in lines that we skip checking."""
+        for line in lines:
+            self.ignored_lines.pop(line, None)
+
     def serialize(self) -> JsonDict:
         return {
             ".class": "MypyFile",
diff --git a/mypy/semanal_pass1.py b/mypy/semanal_pass1.py
index 659f33e65ead..101aab3af141 100644
--- a/mypy/semanal_pass1.py
+++ b/mypy/semanal_pass1.py
@@ -47,7 +47,7 @@ class SemanticAnalyzerPreAnalysis(TraverserVisitor):
 
       def do_stuff():
           # type: () -> None:
-          if sys.python_version < (3,):
+          if sys.version_info < (3,):
               import xyz  # Only available in Python 2
               xyz.whatever()
           ...
@@ -62,7 +62,6 @@ def visit_file(self, file: MypyFile, fnam: str, mod_id: str, options: Options) -
         self.cur_mod_node = file
         self.options = options
         self.is_global_scope = True
-        self.unreachable_lines: set[int] = set()
 
         for i, defn in enumerate(file.defs):
             defn.accept(self)
@@ -74,10 +73,9 @@ def visit_file(self, file: MypyFile, fnam: str, mod_id: str, options: Options) -
                     next_def, last = file.defs[i + 1], file.defs[-1]
                     if last.end_line is not None:
                         # We are on a Python version recent enough to support end lines.
-                        self.unreachable_lines |= set(range(next_def.line, last.end_line + 1))
+                        file.remove_ignored_lines(range(next_def.line, last.end_line + 1))
                 del file.defs[i + 1 :]
                 break
-        file.unreachable_lines = self.unreachable_lines
 
     def visit_func_def(self, node: FuncDef) -> None:
         old_global_scope = self.is_global_scope
@@ -127,7 +125,7 @@ def visit_block(self, b: Block) -> None:
         if b.is_unreachable:
             if b.end_line is not None:
                 # We are on a Python version recent enough to support end lines.
-                self.unreachable_lines |= set(range(b.line, b.end_line + 1))
+                self.cur_mod_node.remove_ignored_lines(range(b.line, b.end_line + 1))
             return
         super().visit_block(b)
 
diff --git a/mypy/server/update.py b/mypy/server/update.py
index 7b439eb0ab9f..439cededda01 100644
--- a/mypy/server/update.py
+++ b/mypy/server/update.py
@@ -986,7 +986,6 @@ def key(node: FineGrainedDeferredNode) -> int:
     manager.errors.set_file_ignored_lines(
         file_node.path, file_node.ignored_lines, options.ignore_errors or state.ignore_all
     )
-    manager.errors.set_unreachable_lines(file_node.path, file_node.unreachable_lines)
 
     targets = set()
     for node in nodes: