diff --git a/example_test.go b/example_test.go
index 6216e18..4bd7632 100644
--- a/example_test.go
+++ b/example_test.go
@@ -504,7 +504,7 @@ func Example_envVarOnly() {
 	defer os.Unsetenv("AUTH_KEY")
 
 	var args struct {
-		AuthKey string `arg:"-,--,env:AUTH_KEY"`
+		AuthKey string `arg:"--,env:AUTH_KEY"`
 	}
 
 	MustParse(&args)
@@ -517,7 +517,7 @@ func Example_envVarOnlyShouldIgnoreFlag() {
 	os.Args = split("./example --=my_key")
 
 	var args struct {
-		AuthKey string `arg:"-,--,env:AUTH_KEY"`
+		AuthKey string `arg:"--,env:AUTH_KEY"`
 	}
 
 	err := Parse(&args)
@@ -530,7 +530,7 @@ func Example_envVarOnlyShouldIgnoreShortFlag() {
 	os.Args = split("./example -=my_key")
 
 	var args struct {
-		AuthKey string `arg:"-,--,env:AUTH_KEY"`
+		AuthKey string `arg:"--,env:AUTH_KEY"`
 	}
 
 	err := Parse(&args)
diff --git a/parse.go b/parse.go
index aee60e7..a85419f 100644
--- a/parse.go
+++ b/parse.go
@@ -360,6 +360,11 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			case strings.HasPrefix(key, "--"):
 				spec.long = key[2:]
 			case strings.HasPrefix(key, "-"):
+				if len(key) != 2 {
+					errs = append(errs, fmt.Sprintf("%s.%s: short arguments must be one character only",
+						t.Name(), field.Name))
+					return false
+				}
 				spec.short = key[1:]
 			case key == "required":
 				spec.required = true
diff --git a/usage.go b/usage.go
index f032149..fb5da75 100644
--- a/usage.go
+++ b/usage.go
@@ -84,9 +84,10 @@ func (p *Parser) writeUsageForSubcommand(w io.Writer, cmd *command) {
 		ancestors = append(ancestors, ancestor.name)
 		ancestor = ancestor.parent
 	}
+	// Print environment only variables
 	for _, spec := range cmd.specs {
 		if spec.short == "" && spec.long == "" {
-			ancestors = append(ancestors, spec.env+"="+strings.ToLower(spec.env)+"_value")
+			ancestors = append(ancestors, "["+spec.env+"="+strings.ToLower(spec.env)+"_value"+"]")
 		}
 	}
 
@@ -283,7 +284,7 @@ func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
 	}
 
 	// write the list of environment only variables
-	if len(shortOptions)+len(longOptions) > 0 || cmd.parent == nil {
+	if len(envOnlyOptions) > 0 {
 		fmt.Fprint(w, "\nEnvironment variables:\n")
 		for _, spec := range envOnlyOptions {
 			p.printEnvOnlyVar(w, spec)
diff --git a/usage_test.go b/usage_test.go
index d5e150f..5ac7757 100644
--- a/usage_test.go
+++ b/usage_test.go
@@ -544,14 +544,18 @@ Options:
 }
 
 func TestUsageWithEnvOptions(t *testing.T) {
-	expectedUsage := "Usage: example [-s SHORT]"
+	expectedUsage := "Usage: [CUSTOM=custom_value] [ENVONLY=envonly_value] example [-s SHORT]"
 
 	expectedHelp := `
-Usage: example [-s SHORT]
+Usage: [CUSTOM=custom_value] [ENVONLY=envonly_value] example [-s SHORT]
 
 Options:
   -s SHORT [env: SHORT]
   --help, -h             display this help and exit
+
+Environment variables:
+  ENVONLY
+  CUSTOM
 `
 	var args struct {
 		Short            string `arg:"--,-s,env"`
@@ -648,10 +652,10 @@ Options:
 }
 
 func TestFailEnvOnly(t *testing.T) {
-	expectedUsage := "Usage: AUTH_KEY=auth_key_value example [--arg ARG]"
+	expectedUsage := "Usage: [AUTH_KEY=auth_key_value] example [--arg ARG]"
 
 	expectedHelp := `
-Usage: AUTH_KEY=auth_key_value example [--arg ARG]
+Usage: [AUTH_KEY=auth_key_value] example [--arg ARG]
 
 Options:
   --arg ARG, -a ARG [env: MY_ARG]
@@ -662,7 +666,7 @@ Environment variables:
 `
 	var args struct {
 		ArgParam string `arg:"-a,--arg,env:MY_ARG"`
-		AuthKey  string `arg:"-,--,env:AUTH_KEY"`
+		AuthKey  string `arg:"--,env:AUTH_KEY"`
 	}
 	p, err := NewParser(Config{Program: "example"}, &args)
 	assert.NoError(t, err)