diff --git a/masque/file/dxf.py b/masque/file/dxf.py
index 8af24e6..24bc6a0 100644
--- a/masque/file/dxf.py
+++ b/masque/file/dxf.py
@@ -130,7 +130,7 @@ def writefile(
     with tmpfile(path) as base_stream:
         streams: Tuple[Any, ...] = (base_stream,)
         if path.suffix == '.gz':
-            gz_stream = cast(IO[bytes], gzip.GzipFile(filename='', mtime=0, fileobj=base_stream))
+            gz_stream = cast(IO[bytes], gzip.GzipFile(filename='', mtime=0, fileobj=base_stream, mode='wb'))
             streams = (gz_stream,) + streams
         else:
             gz_stream = base_stream
diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index cb55a37..966f797 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -145,7 +145,7 @@ def writefile(
     with tmpfile(path) as base_stream:
         streams: Tuple[Any, ...] = (base_stream,)
         if path.suffix == '.gz':
-            stream = cast(IO[bytes], gzip.GzipFile(filename='', mtime=0, fileobj=base_stream))
+            stream = cast(IO[bytes], gzip.GzipFile(filename='', mtime=0, fileobj=base_stream, mode='wb'))
             streams = (stream,) + streams
         else:
             stream = base_stream
diff --git a/masque/file/oasis.py b/masque/file/oasis.py
index ab34852..d0955b5 100644
--- a/masque/file/oasis.py
+++ b/masque/file/oasis.py
@@ -190,7 +190,7 @@ def writefile(
     with tmpfile(path) as base_stream:
         streams: Tuple[Any, ...] = (base_stream,)
         if path.suffix == '.gz':
-            stream = cast(IO[bytes], gzip.GzipFile(filename='', mtime=0, fileobj=base_stream))
+            stream = cast(IO[bytes], gzip.GzipFile(filename='', mtime=0, fileobj=base_stream, mode='wb'))
             streams += (stream,)
         else:
             stream = base_stream