diff --git a/src/protocol/generate_protocol.py b/src/protocol/generate_protocol.py
index cf35f54..a0eb4bc 100644
--- a/src/protocol/generate_protocol.py
+++ b/src/protocol/generate_protocol.py
@@ -69,8 +69,8 @@ def print_protocol():
             True)
 
 def main():
-    if len(sys.argv) != 2:
-        print('Please specify the input file.')
+    if len(sys.argv) != 3:
+        print('Usage: generate_protocol.py <input: protocol.hjson> <output: ProtocolDefinitions.h>')
         return
 
     add_text('#pragma once')
@@ -84,7 +84,7 @@ def main():
     add_text('}}')
     add_text('')
 
-    with open('ProtocolDefinitions.h', 'w') as out_file:
+    with open(sys.argv[2], 'w') as out_file:
         out_file.write(text)
         out_file.close()
 
diff --git a/src/protocol/meson.build b/src/protocol/meson.build
index a3f48d7..da7be9d 100644
--- a/src/protocol/meson.build
+++ b/src/protocol/meson.build
@@ -1,4 +1,4 @@
 protocol_headers = custom_target('ProtocolHeader',
   input   : [ 'generate_protocol.py', 'protocol.hjson' ],
   output  : [ 'ProtocolDefinitions.h' ],
-  command : [ python, '@INPUT@' ])
\ No newline at end of file
+  command : [ python, '@INPUT@', '@OUTPUT@' ])
\ No newline at end of file