2 files changed, 3 insertions, 3 deletions
diff --git a/src/runtime/rune.c b/src/runtime/rune.c
index d705a5e36f..5738ca3646 100644
--- a/src/runtime/rune.c
+++ b/src/runtime/rune.c
@@ -235,9 +235,9 @@ sys·bytestorune(byte *str, int32 off, int32 length, int32 outrune, int32 outcou
 }
 
 void
-sys·stringtorune(string str, int32 off, int32 length, int32 outrune, int32 outcount)
+sys·stringtorune(string str, int32 off, int32 outrune, int32 outcount)
 {
-	outcount = charntorune(&outrune, str->str + off, length);
+	outcount = charntorune(&outrune, str->str + off, str->len - off);
 	FLUSH(&outrune);
 	FLUSH(&outcount);
 }
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index f590472439..f182aebae7 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -293,4 +293,4 @@ void	sys·intstring(int64, string);
  */
 void	sys·readfile(string, string, bool);
 void	sys·bytestorune(byte*, int32, int32, int32, int32);
-void	sys·stringtorune(string, int32, int32, int32, int32);
+void	sys·stringtorune(string, int32, int32, int32);