diff --git a/deepset_cloud_sdk/_s3/upload.py b/deepset_cloud_sdk/_s3/upload.py
index 68e77c3a..86a37b71 100644
--- a/deepset_cloud_sdk/_s3/upload.py
+++ b/deepset_cloud_sdk/_s3/upload.py
@@ -148,6 +148,11 @@ def _build_file_data(
         file_data = aiohttp.FormData(quote_fields=True)
         for key in aws_config.fields:
             file_data.add_field(key, aws_config.fields[key])
+
+        # lower case the suffix on upload
+        suffix = aws_safe_name.split(".")[-1]
+        aws_safe_name.replace(f".{suffix}", f".{suffix.lower()}")
+
         file_data.add_field("file", content, filename=aws_safe_name, content_type="text/plain")
         return file_data
 
diff --git a/deepset_cloud_sdk/_service/files_service.py b/deepset_cloud_sdk/_service/files_service.py
index 6efd44a7..0350419b 100644
--- a/deepset_cloud_sdk/_service/files_service.py
+++ b/deepset_cloud_sdk/_service/files_service.py
@@ -299,7 +299,7 @@ def _validate_file_paths(file_paths: List[Path]) -> None:
         """
         logger.info("Validating file paths and metadata.")
         for file_path in file_paths:
-            if file_path.suffix not in SUPPORTED_TYPE_SUFFIXES:
+            if file_path.suffix.lower() not in SUPPORTED_TYPE_SUFFIXES:
                 raise ValueError(
                     f"Invalid file extension: {file_path.suffix}. Refer to the list of supported file types in `SUPPORTED_TYPE_SUFFIXES`. "
                     "Metadata files should have the `.meta.json` extension."
@@ -383,7 +383,7 @@ def _preprocess_paths(
         file_paths = [
             path
             for path in all_files
-            if path.is_file() and (path.suffix in allowed_file_types and not str(path).endswith(META_SUFFIX))
+            if path.is_file() and (path.suffix.lower() in allowed_file_types and not str(path).endswith(META_SUFFIX))
         ]
         combined_paths = meta_file_path + file_paths
 
diff --git a/tests/unit/service/test_files_service.py b/tests/unit/service/test_files_service.py
index e884b8dd..070521c4 100644
--- a/tests/unit/service/test_files_service.py
+++ b/tests/unit/service/test_files_service.py
@@ -1017,6 +1017,18 @@ class TestValidateFilePaths:
             [Path("/home/user/file1.pptx"), Path("/home/user/file1.pptx.meta.json")],
             [Path("/home/user/file1.xlsx"), Path("/home/user/file1.xlsx.meta.json")],
             [Path("/home/user/file1.xml"), Path("/home/user/file1.xml.meta.json")],
+            [Path("/home/user/file1.Txt"), Path("/home/user/file2.txt")],
+            [Path("/home/user/file1.tXt"), Path("/home/user/file1.json")],
+            [Path("/home/user/file1.txT"), Path("/home/user/file1.txT.meta.json")],
+            [Path("/home/user/file1.PDF"), Path("/home/user/file1.PDF.meta.json")],
+            [Path("/home/user/file1.cSv"), Path("/home/user/file1.cSv.meta.json")],
+            [Path("/home/user/file1.Docx"), Path("/home/user/file1.Docx.meta.json")],
+            [Path("/home/user/file1.htML"), Path("/home/user/file1.htML.meta.json")],
+            [Path("/home/user/file1.Json"), Path("/home/user/file1.Json.meta.json")],
+            [Path("/home/user/file1.mD"), Path("/home/user/file1.mD.meta.json")],
+            [Path("/home/user/file1.ppTx"), Path("/home/user/file1.ppTx.meta.json")],
+            [Path("/home/user/file1.xlSx"), Path("/home/user/file1.xlSx.meta.json")],
+            [Path("/home/user/file1.XMl"), Path("/home/user/file1.XMl.meta.json")],
         ],
     )
     async def test_validate_file_paths(self, file_paths: List[Path], monkeypatch: MonkeyPatch) -> None: