diff --git a/Modules/readline.c b/Modules/readline.c
index 2824105a187..ff7075c6822 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1015,7 +1015,7 @@ static int
 #if defined(_RL_FUNCTION_TYPEDEF)
 on_startup_hook(void)
 #else
-on_startup_hook()
+on_startup_hook(void)
 #endif
 {
     int r;
@@ -1030,7 +1030,7 @@ static int
 #if defined(_RL_FUNCTION_TYPEDEF)
 on_pre_input_hook(void)
 #else
-on_pre_input_hook()
+on_pre_input_hook(void)
 #endif
 {
     int r;