diff --git a/c/cli/mlrcli.c b/c/cli/mlrcli.c
index f26cf1e6d..a139218f9 100644
--- a/c/cli/mlrcli.c
+++ b/c/cli/mlrcli.c
@@ -759,7 +759,7 @@ cli_opts_t* parse_command_line(int argc, char** argv) {
 			popts->quote_json_values_always = TRUE;
 		} else if (streq(argv[argi], "--jflatsep")) {
 			check_arg_count(argv, argi, argc, 2);
-			popts->json_flatten_separator = argv[argi+1];
+			popts->json_flatten_separator = sep_from_arg(argv[argi+1], argv[0]);
 			argi++;
 
 		} else if (streq(argv[argi], "--csv"))      { popts->ifile_fmt = popts->ofile_fmt = "csv";
diff --git a/c/todo.txt b/c/todo.txt
index 2e52a2d91..0bca103f0 100644
--- a/c/todo.txt
+++ b/c/todo.txt
@@ -42,17 +42,14 @@ TOP-OF-LIST SUMMARY
 TOP-OF-LIST DETAILS
 
 * JSON I/O:
-  ! string-preservation for doubles !
-  ! n.b. colon-inside! not just for I/O.
-  ! doc this : wishlist: streamable version with fgetc rather than pointer-math.
-    > no tail -f!
-  ! UT !
-    > mlr --json reshape -i x,y -o item,value rec.json
-    > JSON/join UT. both/left/right json cases.
-  - cmt mlhmmv @ writer ...
-  - unbackslash @ jflatsep
-  - use track-source feature
-  - in-mem UTs
+  - code: leading 0/-0 as needed. & cmt why.
+  - code: use track-source feature
+  - UT: mlr --json reshape -i x,y -o item,value rec.json
+  - UT: JSON/join. both/left/right json cases.
+  - UT: more in-mem
+  - cmt: mlhmmv @ writer ...
+  - doc: n.b. colon-inside! not just for I/O.
+  - doc: wishlist: streamable version with fgetc rather than pointer-math. esp.: no tail -f!
 
 ? env vars??