diff --git a/runconfig/parse.go b/runconfig/parse.go
index cccb761010..2d22ee2799 100644
--- a/runconfig/parse.go
+++ b/runconfig/parse.go
@@ -55,7 +55,7 @@ func Parse(cmd *flag.FlagSet, args []string) (*Config, *HostConfig, *flag.FlagSe
 		flHostname        = cmd.String([]string{"h", "-hostname"}, "", "Container host name")
 		flMemoryString    = cmd.String([]string{"m", "-memory"}, "", "Memory limit")
 		flMemorySwap      = cmd.String([]string{"-memory-swap"}, "", "Total memory (memory + swap), '-1' to disable swap")
-		flUser            = cmd.String([]string{"u", "-user"}, "", "Username or UID")
+		flUser            = cmd.String([]string{"u", "-user"}, "", "Username or UID (format: <name|uid>[:<group|gid>])")
 		flWorkingDir      = cmd.String([]string{"w", "-workdir"}, "", "Working directory inside the container")
 		flCpuShares       = cmd.Int64([]string{"c", "-cpu-shares"}, 0, "CPU shares (relative weight)")
 		flCpuset          = cmd.String([]string{"-cpuset"}, "", "CPUs in which to allow execution (0-3, 0,1)")