diff --git a/docs/man/man1/kubectl-exec.1 b/docs/man/man1/kubectl-exec.1
index 45a2f2da69f..706802a9079 100644
--- a/docs/man/man1/kubectl-exec.1
+++ b/docs/man/man1/kubectl-exec.1
@@ -19,7 +19,7 @@ Execute a command in a container.
 .SH OPTIONS
 .PP
 \fB\-c\fP, \fB\-\-container\fP=""
-    Container name
+    Container name. If omitted, the first container in the pod will be chosen
 
 .PP
 \fB\-h\fP, \fB\-\-help\fP=false
diff --git a/docs/user-guide/kubectl/kubectl_exec.md b/docs/user-guide/kubectl/kubectl_exec.md
index ca3303cfcbd..64c6ef46179 100644
--- a/docs/user-guide/kubectl/kubectl_exec.md
+++ b/docs/user-guide/kubectl/kubectl_exec.md
@@ -41,7 +41,7 @@ Execute a command in a container.
 Execute a command in a container.
 
 ```
-kubectl exec POD -c CONTAINER -- COMMAND [args...]
+kubectl exec POD [-c CONTAINER] -- COMMAND [args...]
 ```
 
 ### Examples
@@ -61,7 +61,7 @@ $ kubectl exec 123456-7890 -c ruby-container -i -t -- bash -il
 ### Options
 
 ```
-  -c, --container="": Container name
+  -c, --container="": Container name. If omitted, the first container in the pod will be chosen
   -h, --help[=false]: help for exec
   -p, --pod="": Pod name
   -i, --stdin[=false]: Pass stdin to the container
diff --git a/pkg/kubectl/cmd/exec.go b/pkg/kubectl/cmd/exec.go
index 4cb2d658654..5c2d18b5091 100644
--- a/pkg/kubectl/cmd/exec.go
+++ b/pkg/kubectl/cmd/exec.go
@@ -53,7 +53,7 @@ func NewCmdExec(f *cmdutil.Factory, cmdIn io.Reader, cmdOut, cmdErr io.Writer) *
 		Executor: &DefaultRemoteExecutor{},
 	}
 	cmd := &cobra.Command{
-		Use:     "exec POD -c CONTAINER -- COMMAND [args...]",
+		Use:     "exec POD [-c CONTAINER] -- COMMAND [args...]",
 		Short:   "Execute a command in a container.",
 		Long:    "Execute a command in a container.",
 		Example: exec_example,
@@ -65,7 +65,7 @@ func NewCmdExec(f *cmdutil.Factory, cmdIn io.Reader, cmdOut, cmdErr io.Writer) *
 	}
 	cmd.Flags().StringVarP(&options.PodName, "pod", "p", "", "Pod name")
 	// TODO support UID
-	cmd.Flags().StringVarP(&options.ContainerName, "container", "c", "", "Container name")
+	cmd.Flags().StringVarP(&options.ContainerName, "container", "c", "", "Container name. If omitted, the first container in the pod will be chosen")
 	cmd.Flags().BoolVarP(&options.Stdin, "stdin", "i", false, "Pass stdin to the container")
 	cmd.Flags().BoolVarP(&options.TTY, "tty", "t", false, "Stdin is a TTY")
 	return cmd