diff --git a/chb/cmdline/reportcmds.py b/chb/cmdline/reportcmds.py
index 79b000da..7285ec29 100644
--- a/chb/cmdline/reportcmds.py
+++ b/chb/cmdline/reportcmds.py
@@ -1662,6 +1662,7 @@ def is_cmd_delegation(po: 'ProofObligation') -> bool:
                 fn_arg["role"] = "input"
                 if fmt_arg_count < len(fmt_string_specs.argspecs):
                     fn_arg["type"] = fmt_string_specs.argspecs[fmt_arg_count].arg_type
+                    fn_arg["format-specifier"] = str(fmt_string_specs.argspecs[fmt_arg_count])
                 fmt_arg_count += 1
             else:
                 fn_arg["role"] = "passthrough"