diff --git a/cmd/puppeth/puppeth.go b/cmd/puppeth/puppeth.go
index f9b8fe481..df3fff51b 100644
--- a/cmd/puppeth/puppeth.go
+++ b/cmd/puppeth/puppeth.go
@@ -49,8 +49,8 @@ func main() {
 		rand.Seed(time.Now().UnixNano())
 
 		network := c.String("network")
-		if strings.Contains(network, " ") || strings.Contains(network, "-") {
-			log.Crit("No spaces or hyphens allowed in network name")
+		if strings.Contains(network, " ") || strings.Contains(network, "-") || strings.ToLower(network) != network {
+			log.Crit("No spaces, hyphens or capital letters allowed in network name")
 		}
 		// Start the wizard and relinquish control
 		makeWizard(c.String("network")).run()
diff --git a/cmd/puppeth/wizard_intro.go b/cmd/puppeth/wizard_intro.go
index 60aa0f7ff..3db9a1087 100644
--- a/cmd/puppeth/wizard_intro.go
+++ b/cmd/puppeth/wizard_intro.go
@@ -61,14 +61,14 @@ func (w *wizard) run() {
 	// Make sure we have a good network name to work with	fmt.Println()
 	// Docker accepts hyphens in image names, but doesn't like it for container names
 	if w.network == "" {
-		fmt.Println("Please specify a network name to administer (no spaces or hyphens, please)")
+		fmt.Println("Please specify a network name to administer (no spaces, hyphens or capital letters please)")
 		for {
 			w.network = w.readString()
-			if !strings.Contains(w.network, " ") && !strings.Contains(w.network, "-") {
+			if !strings.Contains(w.network, " ") && !strings.Contains(w.network, "-") && strings.ToLower(w.network) == w.network {
 				fmt.Printf("\nSweet, you can set this via --network=%s next time!\n\n", w.network)
 				break
 			}
-			log.Error("I also like to live dangerously, still no spaces or hyphens")
+			log.Error("I also like to live dangerously, still no spaces, hyphens or capital letters")
 		}
 	}
 	log.Info("Administering Ethereum network", "name", w.network)