diff --git a/net/gce.sh b/net/gce.sh
index 7e827ef2e..06157f19c 100755
--- a/net/gce.sh
+++ b/net/gce.sh
@@ -37,8 +37,8 @@ Configure a GCE-based testnet
  delete - delete the testnet
 
  common options:
-   -p prefix        - Optional common prefix for instance names to avoid
-                        collisions (default: $prefix)
+   -p [prefix]      - Optional common prefix for instance names to avoid
+                      collisions (default: $prefix)
 
  create-specific options:
    -n [number]      - Number of validator nodes (default: $validatorNodeCount)
@@ -71,7 +71,7 @@ while getopts "h?p:Pi:n:c:z:ga:" opt; do
     usage
     ;;
   p)
-    [[ ${OPTARG//[^A-Za-z0-9]/} == "$OPTARG" ]] || usage "Invalid prefix: \"$OPTARG\", alphanumeric only"
+    [[ ${OPTARG//[^A-Za-z0-9-]/} == "$OPTARG" ]] || usage "Invalid prefix: \"$OPTARG\", alphanumeric only"
     prefix=$OPTARG
     ;;
   P)