diff --git a/staging/src/k8s.io/code-generator/generate-internal-groups.sh b/staging/src/k8s.io/code-generator/generate-internal-groups.sh
index 8c31d933705..e4430b27d5b 100755
--- a/staging/src/k8s.io/code-generator/generate-internal-groups.sh
+++ b/staging/src/k8s.io/code-generator/generate-internal-groups.sh
@@ -114,7 +114,7 @@ if [ "${GENS}" = "all" ] || grep -qw "openapi" <<<"${GENS}"; then
   echo "Generating OpenAPI definitions for ${GROUPS_WITH_VERSIONS} at ${OUTPUT_PKG}/openapi"
   declare -a OPENAPI_EXTRA_PACKAGES
   "${GOPATH}/bin/openapi-gen" \
-           --input-dirs "$(codegen::join , "${EXT_FQ_APIS[@]}" "${OPENAPI_EXTRA_PACKAGES[@]}")" \
+           --input-dirs "$(codegen::join , "${EXT_FQ_APIS[@]}" "${OPENAPI_EXTRA_PACKAGES[@]+"${OPENAPI_EXTRA_PACKAGES[@]}"}")" \
            --input-dirs "k8s.io/apimachinery/pkg/apis/meta/v1,k8s.io/apimachinery/pkg/runtime,k8s.io/apimachinery/pkg/version" \
            --output-package "${OUTPUT_PKG}/openapi" \
            -O zz_generated.openapi \