diff --git a/Source/Unicode.m b/Source/Unicode.m
index 57fc2e7c7..90e7a2397 100644
--- a/Source/Unicode.m
+++ b/Source/Unicode.m
@@ -309,7 +309,7 @@ internal_unicode_enc()
   return unicode_enc;
 }
 
-static char *
+static const char *
 iconv_stringforencoding(NSStringEncoding enc)
 {
   switch (enc)