diff --git a/docling/cli/main.py b/docling/cli/main.py
index 79cc04c6..32d57325 100644
--- a/docling/cli/main.py
+++ b/docling/cli/main.py
@@ -165,7 +165,9 @@ def convert(
         None, "--to", help="Specify output formats. Defaults to Markdown."
     ),
     headers: str = typer.Option(
-        None, "--headers", help="Specify http request headers used when fetching url input sources in the form of a JSON string"
+        None,
+        "--headers",
+        help="Specify http request headers used when fetching url input sources in the form of a JSON string",
     ),
     image_export_mode: Annotated[
         ImageRefMode,
@@ -265,7 +267,7 @@ def convert(
     num_threads: Annotated[int, typer.Option(..., help="Number of threads")] = 4,
     device: Annotated[
         AcceleratorDevice, typer.Option(..., help="Accelerator device")
-    ] = AcceleratorDevice.AUTO
+    ] = AcceleratorDevice.AUTO,
 ):
     if verbose == 0:
         logging.basicConfig(level=logging.WARNING)
@@ -282,15 +284,18 @@ def convert(
     if from_formats is None:
         from_formats = [e for e in InputFormat]
 
+    parsed_headers: Optional[Dict[str, str]] = None
     if headers is not None:
-        headers = json.loads(headers)
+        parsed_headers = json.loads(headers)
 
     with tempfile.TemporaryDirectory() as tempdir:
         input_doc_paths: List[Path] = []
         for src in input_sources:
             try:
                 # check if we can fetch some remote url
-                source = resolve_source_to_path(source=src, headers=headers, workdir=Path(tempdir))
+                source = resolve_source_to_path(
+                    source=src, headers=parsed_headers, workdir=Path(tempdir)
+                )
                 input_doc_paths.append(source)
             except FileNotFoundError:
                 err_console.print(
@@ -396,7 +401,7 @@ def convert(
         start_time = time.time()
 
         conv_results = doc_converter.convert_all(
-            input_doc_paths, headers=headers, raises_on_error=abort_on_error
+            input_doc_paths, headers=parsed_headers, raises_on_error=abort_on_error
         )
 
         output.mkdir(parents=True, exist_ok=True)
diff --git a/docling/datamodel/document.py b/docling/datamodel/document.py
index 64b30467..136428e8 100644
--- a/docling/datamodel/document.py
+++ b/docling/datamodel/document.py
@@ -234,7 +234,11 @@ class _DocumentConversionInput(BaseModel):
         self, format_options: Dict[InputFormat, "FormatOption"]
     ) -> Iterable[InputDocument]:
         for item in self.path_or_stream_iterator:
-            obj = resolve_source_to_stream(item, self.headers) if isinstance(item, str) else item
+            obj = (
+                resolve_source_to_stream(item, self.headers)
+                if isinstance(item, str)
+                else item
+            )
             format = self._guess_format(obj)
             backend: Type[AbstractDocumentBackend]
             if format not in format_options.keys():
diff --git a/docling/document_converter.py b/docling/document_converter.py
index 569f058b..cb073949 100644
--- a/docling/document_converter.py
+++ b/docling/document_converter.py
@@ -186,7 +186,7 @@ class DocumentConverter:
             raises_on_error=raises_on_error,
             max_num_pages=max_num_pages,
             max_file_size=max_file_size,
-            headers=headers
+            headers=headers,
         )
         return next(all_res)
 
@@ -204,9 +204,7 @@ class DocumentConverter:
             max_file_size=max_file_size,
         )
         conv_input = _DocumentConversionInput(
-            path_or_stream_iterator=source,
-            limits=limits,
-            headers=headers
+            path_or_stream_iterator=source, limits=limits, headers=headers
         )
         conv_res_iter = self._convert(conv_input, raises_on_error=raises_on_error)