diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
index 87439320ef70..73d7252729fa 100644
--- a/tools/bpf/bpftool/jit_disasm.c
+++ b/tools/bpf/bpftool/jit_disasm.c
@@ -10,6 +10,8 @@
  * Licensed under the GNU General Public License, version 2.0 (GPLv2)
  */
 
+#define _GNU_SOURCE
+#include <stdio.h>
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -51,11 +53,13 @@ static int fprintf_json(void *out, const char *fmt, ...)
 	char *s;
 
 	va_start(ap, fmt);
+	if (vasprintf(&s, fmt, ap) < 0)
+		return -1;
+	va_end(ap);
+
 	if (!oper_count) {
 		int i;
 
-		s = va_arg(ap, char *);
-
 		/* Strip trailing spaces */
 		i = strlen(s) - 1;
 		while (s[i] == ' ')
@@ -68,11 +72,10 @@ static int fprintf_json(void *out, const char *fmt, ...)
 	} else if (!strcmp(fmt, ",")) {
 		   /* Skip */
 	} else {
-		s = va_arg(ap, char *);
 		jsonw_string(json_wtr, s);
 		oper_count++;
 	}
-	va_end(ap);
+	free(s);
 	return 0;
 }