diff --git a/tests/test_ast_profile.c b/tests/test_ast_profile.c
index 17251e75b..a715ce088 100644
--- a/tests/test_ast_profile.c
+++ b/tests/test_ast_profile.c
@@ -88,7 +88,7 @@ TEST(ast_profile_to_str_null) {
 TEST(ast_profile_to_str_small_buf) {
     cbm_ast_profile_t p = make_profile();
     /* buf too small: should write empty string */
-    char buf[1] = "X";
+    char buf[1] = {'X'};
     cbm_ast_profile_to_str(&p, buf, 0);
     /* 0-length buffer: function should handle gracefully */
     PASS();