diff --git a/bundle_certs b/bundle_certs
index 6ad6d6c3cc0e9d28455e43bc41968b0e7c590047..0d22ca466dc208635d703de92bdc3e805bf14306 100755
--- a/bundle_certs
+++ b/bundle_certs
@@ -50,7 +50,7 @@ unbundle_cert () {
     local certificate
     mkdir -p certs
     awk '/-----BEGIN[A-Z0-9 ]*CERTIFICATE-----/ {n++} \
-        n > 0 {print > "certs/cert" (1+n)}' "$1"
+        n > 0 {print > ("certs/cert" (1+n))}' "$1"
     for certificate in certs/cert*
     do
         [ -f "$certificate" ] || continue