diff --git a/src/common/unicode/case_test.c b/src/common/unicode/case_test.c
index fb159c1c27c..e34f700d9c4 100644
--- a/src/common/unicode/case_test.c
+++ b/src/common/unicode/case_test.c
@@ -329,7 +329,7 @@ tfunc_fold(char *dst, size_t dstsize, const char *src,
 }
 
 static void
-test_convert_case()
+test_convert_case(void)
 {
 	/* test string with no case changes */
 	test_convert(tfunc_lower, "√∞", "√∞");
diff --git a/src/common/unicode/category_test.c b/src/common/unicode/category_test.c
index 2b422001209..ffb9d42d704 100644
--- a/src/common/unicode/category_test.c
+++ b/src/common/unicode/category_test.c
@@ -54,7 +54,7 @@ parse_unicode_version(const char *version)
  * White_Space, and Hex_Digit.
  */
 static void
-icu_test()
+icu_test(void)
 {
 	int			successful = 0;
 	int			pg_skipped_codepoints = 0;