diff --git a/ariba/__init__.py b/ariba/__init__.py
index ca6fc157..57037a35 100644
--- a/ariba/__init__.py
+++ b/ariba/__init__.py
@@ -39,6 +39,7 @@
     'ref_seq_chooser',
     'report',
     'report_filter',
+    'report_flag_expander',
     'scaffold_graph',
     'samtools_variants',
     'sequence_metadata',
diff --git a/ariba/flag.py b/ariba/flag.py
index 201d4e76..f0e91718 100644
--- a/ariba/flag.py
+++ b/ariba/flag.py
@@ -61,3 +61,6 @@ def to_long_string(self):
     def has(self, s):
         return self.flags[s]
 
+
+    def to_comma_separated_string(self):
+        return ','.join([f for f in flags_in_order if self.flags[f]])
diff --git a/ariba/report_flag_expander.py b/ariba/report_flag_expander.py
new file mode 100644
index 00000000..da72fea3
--- /dev/null
+++ b/ariba/report_flag_expander.py
@@ -0,0 +1,37 @@
+import copy
+import sys
+
+import pyfastaq
+
+from ariba import flag
+
+class Error (Exception): pass
+
+class ReportFlagExpander:
+    def __init__(self, infile, outfile):
+        self.infile = infile
+        self.outfile = outfile
+
+
+    def run(self):
+        f_in = pyfastaq.utils.open_file_read(self.infile)
+        f_out = pyfastaq.utils.open_file_write(self.outfile)
+        flag_index = None
+
+        for line in f_in:
+            fields = line.rstrip().split()
+
+            if flag_index is None:
+                try:
+                    flag_index = fields.index('flag')
+                except:
+                    raise Error('"flag" column not found in first line of file ' + self.infile +'. Cannot continue')
+            else:
+                f = flag.Flag(int(fields[flag_index]))
+                fields[flag_index] = f.to_comma_separated_string()
+
+            print(*fields, sep='\t', file=f_out)
+
+        f_in.close()
+        f_out.close()
+
diff --git a/ariba/tasks/__init__.py b/ariba/tasks/__init__.py
index 299f5181..5d501d7c 100644
--- a/ariba/tasks/__init__.py
+++ b/ariba/tasks/__init__.py
@@ -1,5 +1,6 @@
 __all__ = [
     'aln2meta',
+    'expandflag',
     'flag',
     'getref',
     'micplot',
diff --git a/ariba/tasks/expandflag.py b/ariba/tasks/expandflag.py
new file mode 100644
index 00000000..bf257e74
--- /dev/null
+++ b/ariba/tasks/expandflag.py
@@ -0,0 +1,8 @@
+import argparse
+import sys
+import ariba
+
+def run(options):
+    expander = ariba.report_flag_expander.ReportFlagExpander(options.infile, options.outfile)
+    expander.run()
+
diff --git a/ariba/tests/data/report_flag_expander.run.in.tsv b/ariba/tests/data/report_flag_expander.run.in.tsv
new file mode 100644
index 00000000..c1919fa0
--- /dev/null
+++ b/ariba/tests/data/report_flag_expander.run.in.tsv
@@ -0,0 +1,3 @@
+#ariba	column1	flag	foo
+name	1	1	foo
+name	2	27	bar
diff --git a/ariba/tests/data/report_flag_expander.run.out.tsv b/ariba/tests/data/report_flag_expander.run.out.tsv
new file mode 100644
index 00000000..c520cf95
--- /dev/null
+++ b/ariba/tests/data/report_flag_expander.run.out.tsv
@@ -0,0 +1,3 @@
+#ariba	column1	flag	foo
+name	1	assembled	foo
+name	2	assembled,assembled_into_one_contig,complete_gene,unique_contig	bar
diff --git a/ariba/tests/flag_test.py b/ariba/tests/flag_test.py
index 7704965d..5ebe4037 100644
--- a/ariba/tests/flag_test.py
+++ b/ariba/tests/flag_test.py
@@ -64,3 +64,11 @@ def test_has(self):
             self.assertFalse(f.has(x))
             f.add(x)
             self.assertTrue(f.has(x))
+
+
+    def test_to_comma_separated_string(self):
+        '''Test to_comma_separated_string'''
+        f = flag.Flag(27)
+        expected = 'assembled,assembled_into_one_contig,complete_gene,unique_contig'
+        self.assertEqual(expected, f.to_comma_separated_string())
+
diff --git a/ariba/tests/report_flag_expander_test.py b/ariba/tests/report_flag_expander_test.py
new file mode 100644
index 00000000..99f66715
--- /dev/null
+++ b/ariba/tests/report_flag_expander_test.py
@@ -0,0 +1,20 @@
+import unittest
+import os
+import filecmp
+from ariba import report_flag_expander
+
+modules_dir = os.path.dirname(os.path.abspath(report_flag_expander.__file__))
+data_dir = os.path.join(modules_dir, 'tests', 'data')
+
+
+class TestReportFlagExpander(unittest.TestCase):
+    def test_run(self):
+        '''test run'''
+        infile = os.path.join(data_dir, 'report_flag_expander.run.in.tsv')
+        expected = os.path.join(data_dir, 'report_flag_expander.run.out.tsv')
+        tmp_out = 'tmp.report_flag_expander.out.tsv'
+        expander = report_flag_expander.ReportFlagExpander(infile, tmp_out)
+        expander.run()
+        self.assertTrue(filecmp.cmp(expected, tmp_out, shallow=False))
+        os.unlink(tmp_out)
+
diff --git a/scripts/ariba b/scripts/ariba
index 9a76385e..498dddd0 100755
--- a/scripts/ariba
+++ b/scripts/ariba
@@ -29,6 +29,18 @@ subparser_aln2meta.add_argument('outprefix', help='Prefix of output filenames')
 subparser_aln2meta.set_defaults(func=ariba.tasks.aln2meta.run)
 
 
+#---------------------------- expandflag ------------------------------
+subparser_expandflag = subparsers.add_parser(
+    'expandflag',
+    help='Expands flag column of report file',
+    usage='ariba expandflag <in.report.tsv> <out.tsv',
+    description='Expands the flag column in a report file from number to comma-separated list of flag bits',
+)
+
+subparser_expandflag.add_argument('infile', help='Name of input report TSV file')
+subparser_expandflag.add_argument('outfile', help='Name of output report TSV file')
+subparser_expandflag.set_defaults(func=ariba.tasks.expandflag.run)
+
 
 #---------------------------- flag ------------------------------------
 subparser_flag = subparsers.add_parser(