diff --git a/pool.sh b/pool.sh
index b18f545..6fe52b6 100755
--- a/pool.sh
+++ b/pool.sh
@@ -53,6 +53,7 @@ getp() {
 
 create() {
     [ -d "$POOL" ] && abort "Pool \"$POOL\" already exists" || :
+    [ ! "$1" -gt 0 ] && abort "Invalid pool capacity $1" || :
     mkdir -p "$POOL"
     # Write pool status
     maxproc=$1