diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index 575e60e..93449ab 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -57,6 +57,7 @@
  *    %[0][width][u][x|X]L      int64_t/uint64_t
  *    %[0][width|m][u][x|X]A    ngx_atomic_int_t/ngx_atomic_uint_t
  *    %P                        ngx_pid_t
+ *    %M                        ngx_msec_t
  *    %r                        rlim_t
  *    %p                        pointer
  *    %V                        pointer to ngx_str_t
@@ -66,9 +67,6 @@
  *    %c                        char
  *    %%                        %
  *
- *  TODO:
- *    %M                        ngx_msec_t
- *
  *  reserved:
  *    %t                        ptrdiff_t
  *    %S                        null-teminated wchar string
@@ -222,6 +220,11 @@
                 sign = 1;
                 break;
 
+            case 'M':
+                ui64 = (uint64_t) va_arg(args, ngx_msec_t);
+                sign = 0;
+                break;
+
             case 'z':
                 if (sign) {
                     i64 = (int64_t) va_arg(args, ssize_t);