diff --git a/roaring/roaring.go b/roaring/roaring.go
index 8cc856bfc..99f7a06fa 100644
--- a/roaring/roaring.go
+++ b/roaring/roaring.go
@@ -398,6 +398,7 @@ func (b *Bitmap) Intersect(other *Bitmap) *Bitmap {
 // Union returns the bitwise union of b and other.
 func (b *Bitmap) Union(others ...*Bitmap) *Bitmap {
 	output := NewBitmap()
+	output.UnionInPlace(b)
 	output.UnionInPlace(others...)
 	return output
 }