diff --git a/s/build b/s/build
index b59804626..820e330f9 100755
--- a/s/build
+++ b/s/build
@@ -33,6 +33,7 @@ if [ ! -d $ROOT/$BUILD ]; then
   exit
 fi
 
+rm -rf crypto tolua
 git submodule update
 
 echo "build eressea"
diff --git a/s/preview b/s/preview
index 79411aea6..86a4f8918 100755
--- a/s/preview
+++ b/s/preview
@@ -22,6 +22,7 @@ exit $2 # otherwise
 function build() {
 assert_dir $SOURCE
 cd $SOURCE
+rm -rf crypto tolua
 git fetch || abort "failed to update source. do you have local changes?"
 [ -z $1 ] || git checkout $1
 git pull