diff --git a/run-build-functions.sh b/run-build-functions.sh
index b68f899e..b9982dfc 100755
--- a/run-build-functions.sh
+++ b/run-build-functions.sh
@@ -458,7 +458,7 @@ install_dependencies() {
   if [ -f package.json ]
   then
     restore_cwd_cache node_modules "node modules"
-    if [ -f yarn.lock ]
+    if [ "$NETLIFY_USE_YARN" = "true" ] || ([ "$NETLIFY_USE_YARN" != "false" ] && [ -f yarn.lock ]) 
     then
       run_yarn $YARN_VERSION
     else
@@ -471,7 +471,7 @@ install_dependencies() {
   then
     if ! [ $(which bower) ]
     then
-      if [ -f yarn.lock ]
+      if [ "$NETLIFY_USE_YARN" = "true" ] || ([ "$NETLIFY_USE_YARN" != "false" ] && [ -f yarn.lock ]) 
       then
         echo "Installing bower with Yarn"
         yarn add bower