diff --git a/daft/filesystem.py b/daft/filesystem.py
index 45f36c21e8..86849b66c5 100644
--- a/daft/filesystem.py
+++ b/daft/filesystem.py
@@ -102,9 +102,10 @@ def get_filesystem(protocol: str, **kwargs) -> fsspec.AbstractFileSystem:
 
 def get_protocol_from_path(path: str) -> str:
     parsed_scheme = urllib.parse.urlparse(path, allow_fragments=False).scheme
+    parsed_scheme = parsed_scheme.lower()
     if parsed_scheme == "" or parsed_scheme is None:
         return "file"
-    if sys.platform == "win32" and len(parsed_scheme) == 1 and parsed_scheme in string.ascii_letters:
+    if sys.platform == "win32" and len(parsed_scheme) == 1 and ('a' <= parsed_scheme) and (parsed_scheme <= 'z'):
         return "file"
     return parsed_scheme
 
diff --git a/src/daft-io/src/lib.rs b/src/daft-io/src/lib.rs
index 45248bc9c1..d630c97d11 100644
--- a/src/daft-io/src/lib.rs
+++ b/src/daft-io/src/lib.rs
@@ -245,7 +245,7 @@ fn parse_url(input: &str) -> Result<(SourceType, Cow<'_, str>)> {
         "az" | "abfs" => Ok((SourceType::AzureBlob, fixed_input)),
         "gcs" | "gs" => Ok((SourceType::GCS, fixed_input)),
         #[cfg(target_env = "msvc")]
-        _ if scheme.len() == 1 => k((SourceType::File, Cow::Owned(format!("file://{input}")))),
+        _ if scheme.len() == 1 && ("a" <= scheme.as_str() && (scheme.as_str() <= "z")) => Ok((SourceType::File, Cow::Owned(format!("file://{input}")))),
         _ => Err(Error::NotImplementedSource { store: scheme }),
     }
 }