diff --git a/programs/progman/program.c b/programs/progman/program.c
index 347378c..bfbbc89 100644
--- a/programs/progman/program.c
+++ b/programs/progman/program.c
@@ -71,7 +71,7 @@
  *           PROGRAM_RegisterProgramWinClass
  */
 
-ATOM PROGRAM_RegisterProgramWinClass()
+ATOM PROGRAM_RegisterProgramWinClass(void)
 {
   WNDCLASS class;