diff --git a/ext/psych/yaml/emitter.c b/ext/psych/yaml/emitter.c
index cafb550bc5..580a8d2123 100644
--- a/ext/psych/yaml/emitter.c
+++ b/ext/psych/yaml/emitter.c
@@ -2178,7 +2178,7 @@ yaml_emitter_write_block_scalar_hints(yaml_emitter_t *emitter,
         yaml_string_t string)
 {
     char indent_hint[2];
-    char *chomp_hint = NULL;
+    const char *chomp_hint = NULL;
 
     if (IS_SPACE(string) || IS_BREAK(string))
     {