1 files changed, 2 insertions, 1 deletions

diff --git a/xs_io.h b/xs_io.h
index 110b0eb..8fc5d6f 100644
--- a/xs_io.h
+++ b/xs_io.h
@@ -27,7 +27,8 @@ xs_str *xs_readline(FILE *f)
         while ((c = fgetc(f)) != EOF) {
             unsigned char rc = c;
 
-            s = xs_append_m(s, (char *)&rc, 1);
+            if (xs_is_string((char *)&rc))
+                s = xs_append_m(s, (char *)&rc, 1);
 
             if (c == '\n')
                 break;