diff --git a/fragment_internal_test.go b/fragment_internal_test.go
index 548e5f40a..ce7e06da9 100644
--- a/fragment_internal_test.go
+++ b/fragment_internal_test.go
@@ -2572,3 +2572,29 @@ func TestFragmentRowIterator(t *testing.T) {
 		}
 	})
 }
+
+func TestUnionInPlaceMapped(t *testing.T) {
+	f := mustOpenFragment("i", "f", "v", 0, CacheTypeNone)
+	defer f.Clean(t)
+	r0 := rand.New(rand.NewSource(2))
+	r1 := rand.New(rand.NewSource(1))
+	data0 := randPositions(1000000, r0)
+	setBM := roaring.NewBitmap()
+	setBM.OpWriter = nil
+	setBM.Add(data0...)
+	unprotectedWriteToFragment(f, setBM)
+	data1 := randPositions(1000000, r1)
+	setBM2 := roaring.NewBitmap()
+	setBM2.OpWriter = nil
+	setBM2.Add(data1...)
+
+	f.storage.UnionInPlace(setBM2)
+}
+
+func randPositions(n int, r *rand.Rand) []uint64 {
+	ret := make([]uint64, n)
+	for i := 0; i < n; i++ {
+		ret[i] = uint64(r.Int63n(ShardWidth))
+	}
+	return ret
+}
diff --git a/roaring/roaring.go b/roaring/roaring.go
index a34d9347e..818184148 100644
--- a/roaring/roaring.go
+++ b/roaring/roaring.go
@@ -2720,6 +2720,7 @@ func unionBitmapRun(a, b *Container) *Container {
 // unions the run b into the bitmap a, mutating a in place. The n value of
 // a will need to be repaired after the fact.
 func unionBitmapRunInPlace(a, b *Container) {
+	a.unmap()
 	statsHit("union/BitmapRun")
 	for j := 0; j < len(b.runs); j++ {
 		a.bitmapSetRangeIgnoreN(uint64(b.runs[j].start), uint64(b.runs[j].last)+1)
@@ -2867,6 +2868,7 @@ func unionArrayBitmap(a, b *Container) *Container {
 // unions array b into bitmap a, mutating a in place. The n value
 // of a will need to be repaired after the fact.
 func unionBitmapArrayInPlace(a, b *Container) {
+	a.unmap()
 	for _, v := range b.array {
 		a.bitmap[v>>6] |= (uint64(1) << (v % 64))
 	}
@@ -2901,6 +2903,8 @@ func unionBitmapBitmap(a, b *Container) *Container {
 // unions bitmap b into bitmap a, mutating a in place. The n value of
 // a will need to be repaired after the fact.
 func unionBitmapBitmapInPlace(a, b *Container) {
+	a.unmap()
+
 	// local variables added to prevent BCE checks in loop
 	// see https://go101.org/article/bounds-check-elimination.html