diff --git a/tests/helper.bash b/tests/helper.bash
index 0e9be09..decf536 100755
--- a/tests/helper.bash
+++ b/tests/helper.bash
@@ -23,6 +23,8 @@ function gen_webhook() {
 function send_webhook {
     TMPFILE="$(mktemp)"
     echo -n "$2" > $TMPFILE
+    # To prevent race conditions where curl is started while $TMPFILE is still empty
+    sync
 
     # We can make a few attempts, just in case the webserver hasn't started yet
     n=0