diff --git a/config.c b/config.c
index 58d3ed5d37..e323153ae4 100644
--- a/config.c
+++ b/config.c
@@ -523,7 +523,7 @@ static int store_aux(const char* key, const char* value)
 	return 0;
 }
 
-static int write_error()
+static int write_error(void)
 {
 	fprintf(stderr, "Failed to write new configuration file\n");
 
diff --git a/merge-recursive.c b/merge-recursive.c
index 4a82b741ae..c8539ec0ba 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -127,7 +127,7 @@ static void output(int v, const char *fmt, ...)
 	va_end(args);
 }
 
-static void flush_output()
+static void flush_output(void)
 {
 	struct output_buffer *b, *n;
 	for (b = output_list; b; b = n) {
diff --git a/sha1_file.c b/sha1_file.c
index 2b860868f5..eb7fc922d3 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -413,7 +413,7 @@ static size_t peak_pack_mapped;
 static size_t pack_mapped;
 struct packed_git *packed_git;
 
-void pack_report()
+void pack_report(void)
 {
 	fprintf(stderr,
 		"pack_report: getpagesize()            = %10" SZ_FMT "\n"