diff --git a/adb/commandline.c b/adb/commandline.c
index 973932f..4c15232 100644
--- a/adb/commandline.c
+++ b/adb/commandline.c
@@ -129,18 +129,22 @@
         "  adb bugreport                - return all information from the device\n"
         "                                 that should be included in a bug report.\n"
         "\n"
-        "  adb backup [-f <file>] [-apk|-noapk] [-shared|-noshared] [-all] [<packages...>]\n"
-        "                               - Write an archive of the device's data to <file>.\n"
-        "                                 If a -f option is not supplied then the data is\n"
-        "                                 written to \"backup.ab\" in the current directory.\n"
+        "  adb backup [-f <file>] [-apk|-noapk] [-shared|-noshared] [-all] [-system|-nosystem] [<packages...>]\n"
+        "                               - write an archive of the device's data to <file>.\n"
+        "                                 If no -f option is supplied then the data is written\n"
+        "                                 to \"backup.ab\" in the current directory.\n"
         "                                 (-apk|-noapk enable/disable backup of the .apks themselves\n"
         "                                    in the archive; the default is noapk.)\n"
         "                                 (-shared|-noshared enable/disable backup of the device's\n"
         "                                    shared storage / SD card contents; the default is noshared.)\n"
         "                                 (-all means to back up all installed applications)\n"
+        "                                 (-system|-nosystem toggles whether -all automatically includes\n"
+        "                                    system applications; the default is to include system apps)\n"
         "                                 (<packages...> is the list of applications to be backed up.  If\n"
         "                                    the -all or -shared flags are passed, then the package\n"
-        "                                    list is optional.)\n"
+        "                                    list is optional.  Applications explicitly given on the\n"
+        "                                    command line will be included even if -nosystem would\n"
+        "                                    ordinarily cause them to be omitted.)\n"
         "\n"
         "  adb restore <file>           - restore device contents from the <file> backup archive\n"
         "\n"