diff --git a/fx/string.c b/fx/string.c
index 68a584d..6c9976c 100644
--- a/fx/string.c
+++ b/fx/string.c
@@ -301,7 +301,7 @@ static fx_string *string_duplicate(const struct fx_string_p *str)
 	const char *src = string_ptr(str);
 	char *dst = string_ptr(new_str_p);
 
-	memcpy(dst, src, str->s_len);
+	memcpy(dst, src, str->s_len + 1);
 	new_str_p->s_len = str->s_len;
 	new_str_p->s_codepoints = str->s_codepoints;