diff --git a/fs/open_options.go b/fs/open_options.go
index 38a391fb9..84e43045c 100644
--- a/fs/open_options.go
+++ b/fs/open_options.go
@@ -142,7 +142,10 @@ func (o *RangeOption) Decode(size int64) (offset, limit int64) {
 // It also adjusts any SeekOption~s, turning them into absolute
 // RangeOption~s instead.
 func FixRangeOption(options []OpenOption, size int64) {
-	if size == 0 {
+	if size < 0 {
+		// Can't do anything for unknown length objects
+		return
+	} else if size == 0 {
 		// if size 0 then remove RangeOption~s
 		// replacing with a NullOptions~s which won't be rendered
 		for i := range options {
diff --git a/fs/open_options_test.go b/fs/open_options_test.go
index fefd1f906..829f45c19 100644
--- a/fs/open_options_test.go
+++ b/fs/open_options_test.go
@@ -149,6 +149,16 @@ func TestFixRangeOptions(t *testing.T) {
 			in:   []OpenOption{},
 			want: []OpenOption{},
 		},
+		{
+			name: "Unknown size -1",
+			in: []OpenOption{
+				&RangeOption{Start: 1, End: -1},
+			},
+			want: []OpenOption{
+				&RangeOption{Start: 1, End: -1},
+			},
+			size: -1,
+		},
 		{
 			name: "Fetch a range with size=0",
 			in: []OpenOption{