diff --git a/block/cloop.c b/block/cloop.c
index 844665ebc3..55a804f1cc 100644
--- a/block/cloop.c
+++ b/block/cloop.c
@@ -124,12 +124,36 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     for(i=0;i<s->n_blocks;i++) {
+        uint64_t size;
+
         s->offsets[i] = be64_to_cpu(s->offsets[i]);
-        if (i > 0) {
-            uint32_t size = s->offsets[i] - s->offsets[i - 1];
-            if (size > max_compressed_block_size) {
-                max_compressed_block_size = size;
-            }
+        if (i == 0) {
+            continue;
+        }
+
+        if (s->offsets[i] < s->offsets[i - 1]) {
+            error_setg(errp, "offsets not monotonically increasing at "
+                       "index %u, image file is corrupt", i);
+            ret = -EINVAL;
+            goto fail;
+        }
+
+        size = s->offsets[i] - s->offsets[i - 1];
+
+        /* Compressed blocks should be smaller than the uncompressed block size
+         * but maybe compression performed poorly so the compressed block is
+         * actually bigger.  Clamp down on unrealistic values to prevent
+         * ridiculous s->compressed_block allocation.
+         */
+        if (size > 2 * MAX_BLOCK_SIZE) {
+            error_setg(errp, "invalid compressed block size at index %u, "
+                       "image file is corrupt", i);
+            ret = -EINVAL;
+            goto fail;
+        }
+
+        if (size > max_compressed_block_size) {
+            max_compressed_block_size = size;
         }
     }
 
diff --git a/tests/qemu-iotests/075 b/tests/qemu-iotests/075
index 9c00fa8138..d74fb33272 100755
--- a/tests/qemu-iotests/075
+++ b/tests/qemu-iotests/075
@@ -44,6 +44,7 @@ _supported_os Linux
 
 block_size_offset=128
 n_blocks_offset=132
+offsets_offset=136
 
 echo
 echo "== check that the first sector can be read =="
@@ -80,6 +81,20 @@ _use_sample_img simple-pattern.cloop.bz2
 poke_file "$TEST_IMG" "$n_blocks_offset" "\x04\x00\x00\x01"
 $QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== refuse images with non-monotonically increasing offsets =="
+_use_sample_img simple-pattern.cloop.bz2
+poke_file "$TEST_IMG" "$offsets_offset" "\x00\x00\x00\x00\xff\xff\xff\xff"
+poke_file "$TEST_IMG" $((offsets_offset + 8)) "\x00\x00\x00\x00\xff\xfe\x00\x00"
+$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
+
+echo
+echo "== refuse images with invalid compressed block size =="
+_use_sample_img simple-pattern.cloop.bz2
+poke_file "$TEST_IMG" "$offsets_offset" "\x00\x00\x00\x00\x00\x00\x00\x00"
+poke_file "$TEST_IMG" $((offsets_offset + 8)) "\xff\xff\xff\xff\xff\xff\xff\xff"
+$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/075.out b/tests/qemu-iotests/075.out
index 7cdaee15ed..911cd3b4d8 100644
--- a/tests/qemu-iotests/075.out
+++ b/tests/qemu-iotests/075.out
@@ -23,4 +23,12 @@ no file open, try 'help open'
 == refuse images that require too many offsets ===
 qemu-io: can't open device TEST_DIR/simple-pattern.cloop: image requires too many offsets, try increasing block size
 no file open, try 'help open'
+
+== refuse images with non-monotonically increasing offsets ==
+qemu-io: can't open device TEST_DIR/simple-pattern.cloop: offsets not monotonically increasing at index 1, image file is corrupt
+no file open, try 'help open'
+
+== refuse images with invalid compressed block size ==
+qemu-io: can't open device TEST_DIR/simple-pattern.cloop: invalid compressed block size at index 1, image file is corrupt
+no file open, try 'help open'
 *** done