diff --git a/encoding.c b/encoding.c
index 298ff0f1b5..59784673e3 100644
--- a/encoding.c
+++ b/encoding.c
@@ -505,7 +505,7 @@ enc_ascii_compatible_p(VALUE enc)
 }
 
 /*
- * Returns 1 when the encoding is Unicode series other than UTF-7 else 0.
+ * Returns non-zero when the encoding is Unicode series other than UTF-7 else 0.
  */
 int
 rb_enc_unicode_p(rb_encoding *enc)