diff --git a/common/rc b/common/rc
index 333cfb82..52b12898 100644
--- a/common/rc
+++ b/common/rc
@@ -2225,6 +2225,19 @@ _require_odirect()
 	rm -f $testfile 2>&1 > /dev/null
 }
 
+_format_swapfile() {
+	local fname="$1"
+	local sz="$2"
+
+	rm -f "$fname"
+	touch "$fname"
+	chmod 0600 "$fname"
+	# Swap files must be nocow on Btrfs.
+	$CHATTR_PROG +C "$fname" > /dev/null 2>&1
+	_pwrite_byte 0x61 0 "$sz" "$fname" >> $seqres.full
+	mkswap "$fname" >> $seqres.full
+}
+
 # Check that the filesystem supports swapfiles
 _require_scratch_swapfile()
 {
@@ -2234,10 +2247,8 @@ _require_scratch_swapfile()
 	_scratch_mount
 
 	# Minimum size for mkswap is 10 pages
-	local size=$(($(get_page_size) * 10))
+	_format_swapfile "$SCRATCH_MNT/swap" $(($(get_page_size) * 10))
 
-	_pwrite_byte 0x61 0 "$size" "$SCRATCH_MNT/swap" >/dev/null 2>&1
-	mkswap "$SCRATCH_MNT/swap" >/dev/null 2>&1
 	if ! swapon "$SCRATCH_MNT/swap" >/dev/null 2>&1; then
 		_scratch_unmount
 		_notrun "swapfiles are not supported"
diff --git a/tests/generic/356 b/tests/generic/356
index 51eeb652..b4a38f84 100755
--- a/tests/generic/356
+++ b/tests/generic/356
@@ -59,11 +59,12 @@ blocks=160
 blksz=65536
 
 echo "Initialize file"
-echo >> $seqres.full
-_pwrite_byte 0x61 0 $((blocks * blksz)) $testdir/file1 >> $seqres.full
-mkswap -U 27376b42-ff65-42ca-919f-6c9b62292a5c $testdir/file1 >> $seqres.full
+_format_swapfile "$testdir/file1" $((blocks * blksz))
 swapon $testdir/file1
 
+touch "$testdir/file2"
+$CHATTR_PROG +C "$testdir/file2" >/dev/null 2>&1
+
 echo "Try to reflink"
 _cp_reflink $testdir/file1 $testdir/file2 2>&1 | _filter_scratch
 
diff --git a/tests/generic/357 b/tests/generic/357
index 0dd0c10f..9a83a283 100755
--- a/tests/generic/357
+++ b/tests/generic/357
@@ -59,9 +59,9 @@ blocks=160
 blksz=65536
 
 echo "Initialize file"
-echo >> $seqres.full
-_pwrite_byte 0x61 0 $((blocks * blksz)) $testdir/file1 >> $seqres.full
-mkswap -U 27376b42-ff65-42ca-919f-6c9b62292a5c $testdir/file1 >> $seqres.full
+_format_swapfile "$testdir/file1" $((blocks * blksz))
+touch "$testdir/file2"
+$CHATTR_PROG +C "$testdir/file2" >/dev/null 2>&1
 _cp_reflink $testdir/file1 $testdir/file2 2>&1 | _filter_scratch
 
 echo "Try to swapon"