diff --git a/ext/psych/yaml/emitter.c b/ext/psych/yaml/emitter.c
index e052fdbbe0..cafb550bc5 100644
--- a/ext/psych/yaml/emitter.c
+++ b/ext/psych/yaml/emitter.c
@@ -221,7 +221,7 @@ yaml_emitter_write_indent(yaml_emitter_t *emitter);
 
 static int
 yaml_emitter_write_indicator(yaml_emitter_t *emitter,
-        char *indicator, int need_whitespace,
+        const char *indicator, int need_whitespace,
         int is_whitespace, int is_indention);
 
 static int
@@ -1784,7 +1784,7 @@ yaml_emitter_write_indent(yaml_emitter_t *emitter)
 
 static int
 yaml_emitter_write_indicator(yaml_emitter_t *emitter,
-        char *indicator, int need_whitespace,
+        const char *indicator, int need_whitespace,
         int is_whitespace, int is_indention)
 {
     size_t indicator_length;