diff --git a/doc.sh b/doc.sh
index 4c20b7a..5148060 100755
--- a/doc.sh
+++ b/doc.sh
@@ -4,7 +4,11 @@ set -eux
 
 cd $(dirname $0)
 
-rustup run $NIGHTLY_TOOLCHAIN cargo doc
+if [ -s NIGHTLY_TOOLCHAIN ]; then
+	rustup run $NIGHTLY_TOOLCHAIN cargo doc
+else
+	cargo doc
+fi;
 
 # cargo-deadlinks will check any links in docs generated by `cargo doc`.
 # This is useful as rustdoc uses raw links which are error prone.