diff --git a/README.md b/README.md
index 228d517..fcf2d7c 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 Lightweight ISO-6937 to UTF-8 conversion library.
 
 ### SYNOPSIS
-> int xconv(char \*inbuf, char \*outbuf, size\_t outbuflen);
+> size\_t xconv(char \*inbuf, char \*outbuf, size\_t outbuflen);
 
 ### DESCRIPTION
 
diff --git a/xconv.c b/xconv.c
index b454f15..12f137a 100644
--- a/xconv.c
+++ b/xconv.c
@@ -61,7 +61,7 @@ is_utf_sequence(char *s)
 	return 1;
 }
 
-int
+size_t
 xconv(char *src, char *dst, size_t dstlen)
 {
 	size_t len = dstlen - 1;
diff --git a/xconv.h b/xconv.h
index 5871433..43e258e 100644
--- a/xconv.h
+++ b/xconv.h
@@ -1,3 +1,7 @@
 
-int xconv(char *, char *, size_t);
+#ifndef _XCONV_H
+
+size_t xconv(char *, char *, size_t);
+
+#endif