diff --git a/haystack/components/routers/document_type_router.py b/haystack/components/routers/document_type_router.py
index 24b9723b91..99008c2b3a 100644
--- a/haystack/components/routers/document_type_router.py
+++ b/haystack/components/routers/document_type_router.py
@@ -134,9 +134,15 @@ def run(self, documents: list[Document]) -> dict[str, list[Document]]:
             mime_type = doc.meta.get(self.mime_type_meta_field) if self.mime_type_meta_field else None
             file_path = doc.meta.get(self.file_path_meta_field) if self.file_path_meta_field else None
 
+            if not isinstance(mime_type, str):
+                mime_type = None
+
             if mime_type is None and file_path:
                 # if mime_type is not provided, try to guess it from the file path
-                mime_type = _guess_mime_type(Path(file_path))
+                try:
+                    mime_type = _guess_mime_type(Path(file_path))
+                except (TypeError, ValueError):
+                    mime_type = None
 
             matched = False
             if mime_type:
diff --git a/releasenotes/notes/fix-document-type-router-non-str-mime-e4f8b29a1c706d53.yaml b/releasenotes/notes/fix-document-type-router-non-str-mime-e4f8b29a1c706d53.yaml
new file mode 100644
index 0000000000..97943a00e8
--- /dev/null
+++ b/releasenotes/notes/fix-document-type-router-non-str-mime-e4f8b29a1c706d53.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    ``DocumentTypeRouter`` now routes documents whose MIME metadata is not a string to ``unclassified``,
+    instead of raising ``TypeError`` inside ``re.fullmatch``.
diff --git a/test/components/routers/test_document_type_router.py b/test/components/routers/test_document_type_router.py
index 38620a0bf6..951494d2ad 100644
--- a/test/components/routers/test_document_type_router.py
+++ b/test/components/routers/test_document_type_router.py
@@ -191,6 +191,35 @@ def test_run_with_missing_metadata(self):
         assert len(result["unclassified"]) == 3
         assert "text/plain" not in result
 
+    def test_run_with_non_string_mime_type_metadata(self):
+        docs = [
+            Document(content="List mime", meta={"mime_type": ["text/plain"]}),
+            Document(content="Int mime", meta={"mime_type": 123}),
+            Document(content="None mime", meta={"mime_type": None}),
+            Document(content="Valid mime", meta={"mime_type": "text/plain"}),
+        ]
+
+        router = DocumentTypeRouter(mime_type_meta_field="mime_type", mime_types=["text/plain"])
+        result = router.run(documents=docs)
+
+        assert len(result["text/plain"]) == 1
+        assert result["text/plain"][0].content == "Valid mime"
+        assert len(result["unclassified"]) == 3
+
+    def test_run_with_non_string_file_path_metadata(self):
+        docs = [
+            Document(content="List path", meta={"file_path": ["example.txt"]}),
+            Document(content="Int path", meta={"file_path": 123}),
+            Document(content="Valid path", meta={"file_path": "example.txt"}),
+        ]
+
+        router = DocumentTypeRouter(file_path_meta_field="file_path", mime_types=["text/plain"])
+        result = router.run(documents=docs)
+
+        assert len(result["text/plain"]) == 1
+        assert result["text/plain"][0].content == "Valid path"
+        assert len(result["unclassified"]) == 2
+
     def test_run_with_regex_patterns(self):
         docs = [
             Document(content="Plain text", meta={"mime_type": "text/plain"}),