diff --git a/tests/qemu-iotests/243 b/tests/qemu-iotests/243
index 6a19919add..5838c6e89c 100755
--- a/tests/qemu-iotests/243
+++ b/tests/qemu-iotests/243
@@ -29,6 +29,7 @@ status=1	# failure is the default!
 _cleanup()
 {
     _cleanup_test_img
+    rm -f $TEST_IMG.data
 }
 trap "_cleanup; exit \$status" 0 1 2 3 15
 
@@ -57,6 +58,27 @@ for mode in off metadata falloc full; do
 
 done
 
+for mode in off metadata falloc full; do
+
+    echo
+    echo "=== External data file: preallocation=$mode ==="
+    echo
+
+    IMGOPTS="data_file=$TEST_IMG.data,preallocation=$mode" _make_test_img 64M
+
+    echo -n "qcow2 file size: "
+    du -b $TEST_IMG | cut -f1
+    echo -n "data file size:  "
+    du -b $TEST_IMG.data | cut -f1
+
+    # Can't use precise numbers here because they differ between filesystems
+    echo -n "qcow2 disk usage: "
+    [ $(du -B1 $TEST_IMG | cut -f1) -lt 1048576 ] && echo "low" || echo "high"
+    echo -n "data disk usage:  "
+    [ $(du -B1 $TEST_IMG.data | cut -f1) -lt 1048576 ] && echo "low" || echo "high"
+
+done
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/243.out b/tests/qemu-iotests/243.out
index e531753ad1..dcb33fac32 100644
--- a/tests/qemu-iotests/243.out
+++ b/tests/qemu-iotests/243.out
@@ -23,4 +23,36 @@ Disk usage: high
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=full
 File size: 67436544
 Disk usage: high
+
+=== External data file: preallocation=off ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=off
+qcow2 file size: 196616
+data file size:  67108864
+qcow2 disk usage: low
+data disk usage:  low
+
+=== External data file: preallocation=metadata ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=metadata
+qcow2 file size: 327680
+data file size:  67108864
+qcow2 disk usage: low
+data disk usage:  low
+
+=== External data file: preallocation=falloc ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=falloc
+qcow2 file size: 327680
+data file size:  67108864
+qcow2 disk usage: low
+data disk usage:  high
+
+=== External data file: preallocation=full ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=full
+qcow2 file size: 327680
+data file size:  67108864
+qcow2 disk usage: low
+data disk usage:  high
 *** done