diff --git a/tests/qemu-iotests/126 b/tests/qemu-iotests/126
new file mode 100755
index 0000000000000000000000000000000000000000..a2d4d6c73dc4aeab3911cb8da36be254e53f4ad7
--- /dev/null
+++ b/tests/qemu-iotests/126
@@ -0,0 +1,105 @@
+#!/bin/bash
+#
+# Tests handling of colons in filenames (which may be confused with protocol
+# prefixes)
+#
+# Copyright (C) 2017 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+# creator
+owner=mreitz@redhat.com
+
+seq="$(basename $0)"
+echo "QA output created by $seq"
+
+here="$PWD"
+status=1	# failure is the default!
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+
+# Needs backing file support
+_supported_fmt qcow qcow2 qed vmdk
+# This is the default protocol (and we want to test the difference between
+# colons which separate a protocol prefix from the rest and colons which are
+# just part of the filename, so we cannot test protocols which require a prefix)
+_supported_proto file
+_supported_os Linux
+
+echo
+echo '=== Testing plain files ==='
+echo
+
+# A colon after a slash is not a protocol prefix separator
+TEST_IMG="$TEST_DIR/a:b.$IMGFMT" _make_test_img 64M
+_rm_test_img "$TEST_DIR/a:b.$IMGFMT"
+
+# But if you want to be really sure, you can do this
+TEST_IMG="file:$TEST_DIR/a:b.$IMGFMT" _make_test_img 64M
+_rm_test_img "$TEST_DIR/a:b.$IMGFMT"
+
+
+echo
+echo '=== Testing relative backing filename resolution ==='
+echo
+
+BASE_IMG="$TEST_DIR/image:base.$IMGFMT"
+TOP_IMG="$TEST_DIR/image:top.$IMGFMT"
+
+TEST_IMG=$BASE_IMG _make_test_img 64M
+TEST_IMG=$TOP_IMG _make_test_img -b ./image:base.$IMGFMT
+
+# The default cluster size depends on the image format
+TEST_IMG=$TOP_IMG _img_info | grep -v 'cluster_size'
+
+_rm_test_img "$BASE_IMG"
+_rm_test_img "$TOP_IMG"
+
+
+# Do another test where we access both top and base without any slash in them
+echo
+pushd "$TEST_DIR" >/dev/null
+
+BASE_IMG="base.$IMGFMT"
+TOP_IMG="file:image:top.$IMGFMT"
+
+TEST_IMG=$BASE_IMG _make_test_img 64M
+TEST_IMG=$TOP_IMG _make_test_img -b "$BASE_IMG"
+
+TEST_IMG=$TOP_IMG _img_info | grep -v 'cluster_size'
+
+_rm_test_img "$BASE_IMG"
+_rm_test_img "image:top.$IMGFMT"
+
+popd >/dev/null
+
+# Note that we could also do the same test with BASE_IMG=file:image:base.$IMGFMT
+# -- but behavior for that case is a bit strange. Protocol-prefixed paths are
+# in a sense always absolute paths, so such paths will never be combined with
+# the path of the overlay. But since "image:base.$IMGFMT" is actually a
+# relative path, it will always be evaluated relative to qemu's CWD (but not
+# relative to the overlay!). While this is more or less intended, it is still
+# pretty strange and thus not something that is tested here.
+# (The root of the issue is the use of a relative path with a protocol prefix.
+#  This may always give you weird results because in one sense, qemu considers
+#  such paths absolute, whereas in another, they are still relative.)
+
+
+# success, all done
+echo '*** done'
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/126.out b/tests/qemu-iotests/126.out
new file mode 100644
index 0000000000000000000000000000000000000000..50d73080faf84a7ec64a3f13ca6f9988ad5c05f6
--- /dev/null
+++ b/tests/qemu-iotests/126.out
@@ -0,0 +1,23 @@
+QA output created by 126
+
+=== Testing plain files ===
+
+Formatting 'TEST_DIR/a:b.IMGFMT', fmt=IMGFMT size=67108864
+Formatting 'TEST_DIR/a:b.IMGFMT', fmt=IMGFMT size=67108864
+
+=== Testing relative backing filename resolution ===
+
+Formatting 'TEST_DIR/image:base.IMGFMT', fmt=IMGFMT size=67108864
+Formatting 'TEST_DIR/image:top.IMGFMT', fmt=IMGFMT size=67108864 backing_file=./image:base.IMGFMT
+image: TEST_DIR/image:top.IMGFMT
+file format: IMGFMT
+virtual size: 64M (67108864 bytes)
+backing file: ./image:base.IMGFMT (actual path: TEST_DIR/./image:base.IMGFMT)
+
+Formatting 'base.IMGFMT', fmt=IMGFMT size=67108864
+Formatting 'file:image:top.IMGFMT', fmt=IMGFMT size=67108864 backing_file=base.IMGFMT
+image: ./image:top.IMGFMT
+file format: IMGFMT
+virtual size: 64M (67108864 bytes)
+backing file: base.IMGFMT (actual path: ./base.IMGFMT)
+*** done
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index 7d86715aae764c44ea56091a4156319bbaf1b4c4..40bef995fea9f3b3ad64999b79e5e7a05b873310 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -130,6 +130,7 @@
 122 rw auto
 123 rw auto quick
 124 rw auto backing
+126 rw auto backing
 128 rw auto quick
 129 rw auto quick
 130 rw auto quick