diff --git a/internal/backend/mem/mem_backend.go b/internal/backend/mem/mem_backend.go
index 950ae122d..719ca46a5 100644
--- a/internal/backend/mem/mem_backend.go
+++ b/internal/backend/mem/mem_backend.go
@@ -81,14 +81,14 @@ func (be *MemoryBackend) Save(ctx context.Context, h restic.Handle, rd restic.Re
 		return err
 	}
 
-	be.data[h] = buf
-	debug.Log("saved %v bytes at %v", len(buf), h)
-
 	// sanity check
 	if int64(len(buf)) != rd.Length() {
 		return errors.Errorf("wrote %d bytes instead of the expected %d bytes", len(buf), rd.Length())
 	}
 
+	be.data[h] = buf
+	debug.Log("saved %v bytes at %v", len(buf), h)
+
 	return ctx.Err()
 }
 
diff --git a/internal/backend/test/tests.go b/internal/backend/test/tests.go
index a35b75e5a..ae9b58677 100644
--- a/internal/backend/test/tests.go
+++ b/internal/backend/test/tests.go
@@ -577,13 +577,15 @@ func (s *Suite) TestSaveError(t *testing.T) {
 	}()
 
 	length := rand.Intn(1<<23) + 200000
-	data := test.Random(23, length)
+	data := test.Random(24, length)
 	var id restic.ID
 	copy(id[:], data)
 
 	// test that incomplete uploads fail
 	h := restic.Handle{Type: restic.PackFile, Name: id.String()}
 	err := b.Save(context.TODO(), h, &incompleteByteReader{ByteReader: *restic.NewByteReader(data)})
+	// try to delete possible leftovers
+	_ = s.delayedRemove(t, b, h)
 	if err == nil {
 		t.Fatal("incomplete upload did not fail")
 	}