on_message raising SyntaxError when called

This code normally works for me when I use it, but it stopped working. First with other async definitions, but now on_message isn’t working!

async def on_ready():
    print("WizBot is currently online! Go check your Discord server; the bot should be active."

@client.event
async def on_message(message):
    if message.author == client.user:
        return
    if message.content.startswith('+test'):
        await message.channel.send('WizBot is up and running!')

WizBot is the name of my bot.Also if it is helpful, I am using repl.it. on_ready() works though, but I get a pyflakes SyntaxError for the d in the def on_message(message).
View error message

File "main.py", line 21
    async def on_message(message):
          ^
SyntaxError: invalid syntax

Can someone help?