diff --git a/setup.cfg b/setup.cfg
index 9dbf634..1db7a2d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -28,7 +28,7 @@ packages =
     zope-stubs
 package_dir = =src
 install_requires =
-    mypy>=1.0.0,<1.6.0
+    mypy>=1.0.0,<1.8.0
     zope.interface
     zope.schema
 include_package_data = True
diff --git a/src/mypy_zope/plugin.py b/src/mypy_zope/plugin.py
index fcf0999..a285c77 100644
--- a/src/mypy_zope/plugin.py
+++ b/src/mypy_zope/plugin.py
@@ -496,7 +496,7 @@ def _get_metadata(self, typeinfo: TypeInfo) -> Dict[str, Any]:
 
     def _is_interface(self, typeinfo: TypeInfo) -> bool:
         md = self._get_metadata(typeinfo)
-        return md.get("is_interface", False)
+        return cast(bool, md.get("is_interface", False))
 
     def _adjust_interface_function(
         self,