diff --git a/tests/qemu-iotests/common b/tests/qemu-iotests/common
index 5795358924..37e3bed40c 100644
--- a/tests/qemu-iotests/common
+++ b/tests/qemu-iotests/common
@@ -137,6 +137,7 @@ common options
 check options
     -raw                test raw (default)
     -cow                test cow
+    -cloop              test cloop
     -qcow               test qcow
     -qcow2              test qcow2
     -qed                test qed
@@ -178,6 +179,12 @@ testlist options
             xpand=false
             ;;
 
+        -cloop)
+            IMGFMT=cloop
+            IMGFMT_GENERIC=false
+            xpand=false
+            ;;
+
         -qcow)
             IMGFMT=qcow
             xpand=false
diff --git a/tests/qemu-iotests/common.rc b/tests/qemu-iotests/common.rc
index 881079bdb9..7f00883cad 100644
--- a/tests/qemu-iotests/common.rc
+++ b/tests/qemu-iotests/common.rc
@@ -364,6 +364,9 @@ _fail()
 #
 _supported_fmt()
 {
+    # "generic" is suitable for most image formats. For some formats it doesn't
+    # work, however (most notably read-only formats), so they can opt out by
+    # setting IMGFMT_GENERIC to false.
     for f; do
         if [ "$f" = "$IMGFMT" -o "$f" = "generic" -a "$IMGFMT_GENERIC" = "true" ]; then
             return