diff --git a/bfxapi/rest/bfx_rest.py b/bfxapi/rest/bfx_rest.py
index af9462f..92f27ed 100644
--- a/bfxapi/rest/bfx_rest.py
+++ b/bfxapi/rest/bfx_rest.py
@@ -874,7 +874,7 @@ class BfxRest:
         message = await self.post(endpoint, payload)
         return message
 
-    async def generate_invoice(self, wallet='exchange', currency='LNX', amount=None):
+    async def generate_invoice(self, amount, wallet='exchange', currency='LNX'):
         """
         Generates a Lightning Network deposit invoice