diff --git a/internal/r2/r2.go b/internal/r2/r2.go
index 0437864..cd2ffa9 100644
--- a/internal/r2/r2.go
+++ b/internal/r2/r2.go
@@ -1,6 +1,7 @@
 package r2
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -48,11 +49,19 @@ func (c *Client) Upload(ctx context.Context, key, contentType string, size int64
 }
 
 func (c *Client) uploadSimple(ctx context.Context, key, contentType string, body io.Reader) error {
-	_, err := c.s3.PutObject(ctx, &s3.PutObjectInput{
-		Bucket:      &c.bucket,
-		Key:         &key,
-		Body:        body,
-		ContentType: &contentType,
+	// R2 requires Content-Length; buffer the body so we can set it.
+	// Only used for files < 100MB, so memory usage is bounded.
+	data, err := io.ReadAll(body)
+	if err != nil {
+		return fmt.Errorf("read body: %w", err)
+	}
+	size := int64(len(data))
+	_, err = c.s3.PutObject(ctx, &s3.PutObjectInput{
+		Bucket:        &c.bucket,
+		Key:           &key,
+		Body:          bytes.NewReader(data),
+		ContentType:   &contentType,
+		ContentLength: &size,
 	})
 	return err
 }
@@ -78,12 +87,16 @@ func (c *Client) uploadMultipart(ctx context.Context, key, contentType string, b
 			break
 		}
 
+		partData := make([]byte, n)
+		copy(partData, buf[:n])
+		partLen := int64(n)
 		upload, err := c.s3.UploadPart(ctx, &s3.UploadPartInput{
-			Bucket:     &c.bucket,
-			Key:        &key,
-			UploadId:   uploadID,
-			PartNumber: &partNum,
-			Body:       io.NopCloser(io.LimitReader(bytesReader(buf[:n]), int64(n))),
+			Bucket:        &c.bucket,
+			Key:           &key,
+			UploadId:      uploadID,
+			PartNumber:    &partNum,
+			Body:          bytes.NewReader(partData),
+			ContentLength: &partLen,
 		})
 		if err != nil {
 			c.s3.AbortMultipartUpload(ctx, &s3.AbortMultipartUploadInput{
@@ -147,24 +160,3 @@ func (c *Client) Delete(ctx context.Context, key string) error {
 	return err
 }
 
-// bytesReader wraps a byte slice as an io.Reader.
-type bytesReaderImpl struct {
-	data []byte
-	pos  int
-}
-
-func bytesReader(b []byte) io.Reader {
-	// Make a copy so the buffer can be reused
-	cp := make([]byte, len(b))
-	copy(cp, b)
-	return &bytesReaderImpl{data: cp}
-}
-
-func (r *bytesReaderImpl) Read(p []byte) (int, error) {
-	if r.pos >= len(r.data) {
-		return 0, io.EOF
-	}
-	n := copy(p, r.data[r.pos:])
-	r.pos += n
-	return n, nil
-}
diff --git a/web/index.html b/web/index.html
index 70fdb0a..589c544 100644
--- a/web/index.html
+++ b/web/index.html
@@ -28,7 +28,7 @@
                 <label for="slug">Custom URL</label>
                 <div class="slug-input">
                     <span class="slug-prefix">/f/</span>
-                    <input type="text" id="slug" placeholder="my-file" pattern="[a-zA-Z0-9][a-zA-Z0-9._-]*" maxlength="64">
+                    <input type="text" id="slug" placeholder="my-file" pattern="[a-zA-Z0-9][a-zA-Z0-9.\-_]*" maxlength="64">
                 </div>
             </div>
             <div class="option-group">