diff --git a/pkgs/development/compilers/dart/update.sh b/pkgs/development/compilers/dart/update.sh
index 87f430cd5d2d..38940a696b19 100755
--- a/pkgs/development/compilers/dart/update.sh
+++ b/pkgs/development/compilers/dart/update.sh
@@ -17,8 +17,11 @@ SRC_FILE=$(mktemp)
 
 log "file to write is $SRC_FILE"
 
-PRELUDE="let version = \"$NEW_VER\"; in
-{ fetchurl }: {
+PRELUDE="let
+  version = \"$NEW_VER\";
+in
+{ fetchurl }:
+{
   versionUsed = version;"
 echo "$PRELUDE" > "$SRC_FILE"
 log "wrote prelude"