diff --git a/src/guarddoc/scanners/archive.py b/src/guarddoc/scanners/archive.py
index 4e74aa9..2485ccf 100644
--- a/src/guarddoc/scanners/archive.py
+++ b/src/guarddoc/scanners/archive.py
@@ -56,13 +56,11 @@ class ArchiveScanner(BaseScanner):
     def name(self) -> str:
         return "ArchiveScanner"
 
-    def is_supported(self, file_path: Path, mime_type: str) -> bool:
+    def is_supported(self, file_path: Path, mime_type: str | None) -> bool:
         ext = file_path.suffix.lower()
+        mime = (mime_type or "").lower()
         return (
-            ext in self.ARCHIVE_EXTENSIONS
-            or "zip" in mime_type
-            or "tar" in mime_type
-            or "compressed" in mime_type
+            ext in self.ARCHIVE_EXTENSIONS or "zip" in mime or "tar" in mime or "compressed" in mime
         )
 
     def scan(
diff --git a/src/guarddoc/scanners/office.py b/src/guarddoc/scanners/office.py
index a2280c1..bf1fedc 100644
--- a/src/guarddoc/scanners/office.py
+++ b/src/guarddoc/scanners/office.py
@@ -26,12 +26,11 @@ class OfficeScanner(BaseScanner):
         ".pptm",
     }
 
-    def is_supported(self, file_path: Path, mime_type: str = "unknown") -> bool:
+    def is_supported(self, file_path: Path, mime_type: str | None) -> bool:
         """Check if file extension or MIME type matches Microsoft Office documents."""
         ext = file_path.suffix.lower()
-        return (
-            ext in self.OFFICE_EXTENSIONS or "officedocument" in mime_type or "msword" in mime_type
-        )
+        mime = (mime_type or "").lower()
+        return ext in self.OFFICE_EXTENSIONS or "officedocument" in mime or "msword" in mime
 
     def scan(
         self,