diff --git a/block/qcow2.c b/block/qcow2.c
index 10eccf91e1..7809f5cab4 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -460,6 +460,18 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
 
     s->qcow_version = header.version;
 
+    /* Initialise cluster size */
+    if (header.cluster_bits < MIN_CLUSTER_BITS ||
+        header.cluster_bits > MAX_CLUSTER_BITS) {
+        error_setg(errp, "Unsupported cluster size: 2^%i", header.cluster_bits);
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    s->cluster_bits = header.cluster_bits;
+    s->cluster_size = 1 << s->cluster_bits;
+    s->cluster_sectors = 1 << (s->cluster_bits - 9);
+
     /* Initialise version 3 header fields */
     if (header.version == 2) {
         header.incompatible_features    = 0;
@@ -473,6 +485,18 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
         be64_to_cpus(&header.autoclear_features);
         be32_to_cpus(&header.refcount_order);
         be32_to_cpus(&header.header_length);
+
+        if (header.header_length < 104) {
+            error_setg(errp, "qcow2 header too short");
+            ret = -EINVAL;
+            goto fail;
+        }
+    }
+
+    if (header.header_length > s->cluster_size) {
+        error_setg(errp, "qcow2 header exceeds cluster size");
+        ret = -EINVAL;
+        goto fail;
     }
 
     if (header.header_length > sizeof(header)) {
@@ -530,12 +554,6 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     }
     s->refcount_order = header.refcount_order;
 
-    if (header.cluster_bits < MIN_CLUSTER_BITS ||
-        header.cluster_bits > MAX_CLUSTER_BITS) {
-        error_setg(errp, "Unsupported cluster size: 2^%i", header.cluster_bits);
-        ret = -EINVAL;
-        goto fail;
-    }
     if (header.crypt_method > QCOW_CRYPT_AES) {
         error_setg(errp, "Unsupported encryption method: %i",
                    header.crypt_method);
@@ -546,9 +564,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     if (s->crypt_method_header) {
         bs->encrypted = 1;
     }
-    s->cluster_bits = header.cluster_bits;
-    s->cluster_size = 1 << s->cluster_bits;
-    s->cluster_sectors = 1 << (s->cluster_bits - 9);
+
     s->l2_bits = s->cluster_bits - 3; /* L2 is always one cluster */
     s->l2_size = 1 << s->l2_bits;
     bs->total_sectors = header.size / 512;
diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
new file mode 100755
index 0000000000..6512701e1e
--- /dev/null
+++ b/tests/qemu-iotests/080
@@ -0,0 +1,61 @@
+#!/bin/bash
+#
+# qcow2 format input validation tests
+#
+# Copyright (C) 2013 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=kwolf@redhat.com
+
+seq=`basename $0`
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+
+_cleanup()
+{
+	_cleanup_test_img
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+
+_supported_fmt qcow2
+_supported_proto generic
+_supported_os Linux
+
+header_size=104
+offset_header_size=100
+offset_ext_magic=$header_size
+offset_ext_size=$((header_size + 4))
+
+echo
+echo "== Huge header size =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_header_size" "\xff\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+poke_file "$TEST_IMG" "$offset_header_size" "\x7f\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
+# success, all done
+echo "*** done"
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
new file mode 100644
index 0000000000..41a166a27f
--- /dev/null
+++ b/tests/qemu-iotests/080.out
@@ -0,0 +1,9 @@
+QA output created by 080
+
+== Huge header size ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow2: qcow2 header exceeds cluster size
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow2: qcow2 header exceeds cluster size
+no file open, try 'help open'
+*** done
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index 9c99edc449..ed44f355af 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -85,6 +85,7 @@
 077 rw auto quick
 078 rw auto
 079 rw auto
+080 rw auto
 081 rw auto
 082 rw auto quick
 083 rw auto