diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index 753238354f6d36..3e1c3cf25d8405 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -90,6 +90,8 @@ def add_type(self, type, ext, strict=True):
         list of standard types, else to the list of non-standard
         types.
         """
+        if not type:
+            return
         self.types_map[strict][ext] = type
         exts = self.types_map_inv[strict].setdefault(type, [])
         if ext not in exts:
diff --git a/Misc/NEWS.d/next/Library/2025-01-15-12-04-30.gh-issue-128703.6WPf38.rst b/Misc/NEWS.d/next/Library/2025-01-15-12-04-30.gh-issue-128703.6WPf38.rst
new file mode 100644
index 00000000000000..1e6af90bc04b63
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-01-15-12-04-30.gh-issue-128703.6WPf38.rst
@@ -0,0 +1,2 @@
+Fix :func:`mimetypes.guess_type` to use default mapping for empty
+``Content-Type`` in registry.