diff --git a/src/libstrongswan/utils/printf_hook/printf_hook_builtin.c b/src/libstrongswan/utils/printf_hook/printf_hook_builtin.c
index 466c673..219c7bd 100644
--- a/src/libstrongswan/utils/printf_hook/printf_hook_builtin.c
+++ b/src/libstrongswan/utils/printf_hook/printf_hook_builtin.c
@@ -843,14 +843,14 @@ int builtin_vsnprintf(char *buffer, size_t n, const char *format, va_list ap)
 								/* String */
 								sarg = va_arg(ap, const char *);
 								sarg = sarg ? sarg : "(null)";
-								slen = strlen(sarg);
+								slen = prec ? strnlen(sarg, prec) : strlen(sarg);
 								goto is_string;
 							}
 							case 'm':
 							{
 								/* glibc error string */
 								sarg = strerror(errno);
-								slen = strlen(sarg);
+								slen = prec ? strnlen(sarg, prec) : strlen(sarg);
 								goto is_string;
 							}
 							is_string: