diff --git a/ceilometerclient/v2/shell.py b/ceilometerclient/v2/shell.py
index d5bddf5..9be9b02 100644
--- a/ceilometerclient/v2/shell.py
+++ b/ceilometerclient/v2/shell.py
@@ -144,7 +144,8 @@ def do_sample_list(cc, args):
 @utils.arg('--sample-volume', metavar='<SAMPLE_VOLUME>', required=True,
            help='The sample volume.')
 @utils.arg('--resource-metadata', metavar='<RESOURCE_METADATA>',
-           help='Resource metadata.')
+           help='Resource metadata. Provided value should be a set of '
+                'key-value pairs e.g. {"key":"value"}.')
 @utils.arg('--timestamp', metavar='<TIMESTAMP>',
            help='The sample timestamp.')
 def do_sample_create(cc, args={}):