diff --git a/scripts/lib.sh b/scripts/lib.sh
index e078a24b1..138672ae1 100755
--- a/scripts/lib.sh
+++ b/scripts/lib.sh
@@ -280,7 +280,7 @@ elif [ "$OSNAME" == "ubuntu"  ] || [ "$OSNAME" == "debian" ]; then
 
     apt install -y libxml2-dev gcc build-essential openssl make libssl-dev 
     apt install -y libxml2 curl libcurl4-gnutls-dev libjpeg-dev libpng-dev libmcrypt-dev
-    apt install -y graphviz bison re2c
+    apt install -y graphviz bison re2c flex
     apt install -y libsqlite3-dev libcurl4-openssl-dev curl
     apt install -y libonig-dev