diff --git a/docling/datamodel/document.py b/docling/datamodel/document.py
index 668e8249..64ff4ac8 100644
--- a/docling/datamodel/document.py
+++ b/docling/datamodel/document.py
@@ -302,7 +302,7 @@ class _DocumentConversionInput(BaseModel):
                     if ("." in obj.name and not obj.name.startswith("."))
                     else ""
                 )
-                mime = _DocumentConversionInput._mime_from_extension(ext)
+                mime = _DocumentConversionInput._mime_from_extension(ext.lower())
 
         mime = mime or _DocumentConversionInput._detect_html_xhtml(content)
         mime = mime or _DocumentConversionInput._detect_csv(content)
@@ -368,6 +368,8 @@ class _DocumentConversionInput(BaseModel):
             mime = FormatToMimeType[InputFormat.JSON_DOCLING][0]
         elif ext in FormatToExtensions[InputFormat.PDF]:
             mime = FormatToMimeType[InputFormat.PDF][0]
+        elif ext in FormatToExtentions[InputFormat.DOCX]:
+            mime = FormatToMimeType[InputFormat.DOCX][0]
         return mime
 
     @staticmethod