diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index f800fc95f5d714dfaf60c0a16143083e69668d03..473887d1d61afec03b58f153556a50424f97a0b2 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -802,7 +802,7 @@ static const struct option options[] = {
 	OPT_STRING('s', "sort", &sort_order, "key[,key2...]",
 		   "sort by key(s): pid, comm, dso, symbol, parent, cpu, srcline, ..."
 		   " Please refer the man page for the complete list."),
-	OPT_STRING('t', "field-separator", &symbol_conf.field_sep, "separator",
+	OPT_STRING_NOEMPTY('t', "field-separator", &symbol_conf.field_sep, "separator",
 		   "separator for columns, no spaces will be added between "
 		   "columns '.' is reserved."),
 	OPT_STRING(0, "symfs", &symbol_conf.symfs, "directory",
diff --git a/tools/perf/builtin-mem.c b/tools/perf/builtin-mem.c
index 46c69318de84d4f5f854f7d971c61f6d1b4ea3e4..b4dcf0bfc0299c438f8e7de5f561025693c01a90 100644
--- a/tools/perf/builtin-mem.c
+++ b/tools/perf/builtin-mem.c
@@ -286,7 +286,7 @@ int cmd_mem(int argc, const char **argv, const char *prefix __maybe_unused)
 		   "input file name"),
 	OPT_STRING('C', "cpu", &mem.cpu_list, "cpu",
 		   "list of cpus to profile"),
-	OPT_STRING('x', "field-separator", &symbol_conf.field_sep,
+	OPT_STRING_NOEMPTY('x', "field-separator", &symbol_conf.field_sep,
 		   "separator",
 		   "separator for columns, no spaces will be added"
 		   " between columns '.' is reserved."),