diff --git a/src/plugins/e-acsl/tests/format/oracle/gen_fprintf.c b/src/plugins/e-acsl/tests/format/oracle/gen_fprintf.c
index 09cc47807a43a2a0b3fbd0c492fcbd3c7da99701..8181cbdca07bfae87d351207f714b53944dd43f2 100644
--- a/src/plugins/e-acsl/tests/format/oracle/gen_fprintf.c
+++ b/src/plugins/e-acsl/tests/format/oracle/gen_fprintf.c
@@ -36,7 +36,7 @@ char *__gen_e_acsl_literal_string_18;
 char *__gen_e_acsl_literal_string_17;
 /*@ assigns \result;
     assigns \result \from \nothing; */
-extern int ( /* missing proto */ fork)();
+extern int ( /* missing proto */ fork)(void);
 
 void __e_acsl_globals_init(void)
 {