diff --git a/tests/qemu-iotests/005 b/tests/qemu-iotests/005
index 58442762fe..b6d03ac37d 100755
--- a/tests/qemu-iotests/005
+++ b/tests/qemu-iotests/005
@@ -59,10 +59,7 @@ fi
 # Sanity check: For raw, we require a file system that permits the creation
 # of a HUGE (but very sparse) file. Check we can create it before continuing.
 if [ "$IMGFMT" = "raw" ]; then
-    if ! truncate --size=5T "$TEST_IMG"; then
-        _notrun "file system on $TEST_DIR does not support large enough files"
-    fi
-    rm "$TEST_IMG"
+    _require_large_file 5T
 fi
 
 echo
diff --git a/tests/qemu-iotests/220 b/tests/qemu-iotests/220
index 2d62c5dcac..15159270d3 100755
--- a/tests/qemu-iotests/220
+++ b/tests/qemu-iotests/220
@@ -42,10 +42,8 @@ echo "== Creating huge file =="
 
 # Sanity check: We require a file system that permits the creation
 # of a HUGE (but very sparse) file.  tmpfs works, ext4 does not.
-if ! truncate --size=513T "$TEST_IMG"; then
-    _notrun "file system on $TEST_DIR does not support large enough files"
-fi
-rm "$TEST_IMG"
+_require_large_file 513T
+
 IMGOPTS='cluster_size=2M,refcount_bits=1' _make_test_img 513T
 
 echo "== Populating refcounts =="
diff --git a/tests/qemu-iotests/common.rc b/tests/qemu-iotests/common.rc
index 0cc8acc9ed..6f0582c79a 100644
--- a/tests/qemu-iotests/common.rc
+++ b/tests/qemu-iotests/common.rc
@@ -643,5 +643,15 @@ _require_drivers()
     done
 }
 
+# Check that we have a file system that allows huge (but very sparse) files
+#
+_require_large_file()
+{
+    if ! truncate --size="$1" "$TEST_IMG"; then
+        _notrun "file system on $TEST_DIR does not support large enough files"
+    fi
+    rm "$TEST_IMG"
+}
+
 # make sure this script returns success
 true