diff --git a/missing/langinfo.c b/missing/langinfo.c
index 9ba06b15f6..0274a378f5 100644
--- a/missing/langinfo.c
+++ b/missing/langinfo.c
@@ -140,7 +140,7 @@ char *nl_langinfo(nl_item item)
 
 #ifdef TEST
 #include <stdio.h>
-int main()
+int main(void)
 {
   printf("%s\n", nl_langinfo(CODESET));
   return 0;
diff --git a/thread.c b/thread.c
index 17510b32f2..1209de948a 100644
--- a/thread.c
+++ b/thread.c
@@ -5751,7 +5751,7 @@ rb_set_coverages(VALUE coverages, int mode, VALUE me2counter)
 }
 
 void
-rb_resume_coverages()
+rb_resume_coverages(void)
 {
     int mode = GET_VM()->coverage_mode;
     VALUE me2counter = GET_VM()->me2counter;
@@ -5765,7 +5765,7 @@ rb_resume_coverages()
 }
 
 void
-rb_suspend_coverages()
+rb_suspend_coverages(void)
 {
     rb_remove_event_hook((rb_event_hook_func_t) update_line_coverage);
     if (GET_VM()->coverage_mode & COVERAGE_TARGET_BRANCHES) {