diff --git a/selection.c b/selection.c
index 602377f..54db131 100644
--- a/selection.c
+++ b/selection.c
@@ -472,8 +472,11 @@ LIB3270_EXPORT char * lib3270_get_text(H3270 *h, int offset, int len)
 	}
 
 	maxlen = (h->rows * (h->cols+1)) - offset;
-	if(maxlen <= 0 || offset < 0)
+	if(maxlen <= 0 || offset < 0)
+	{
+		errno = EINVAL;
 		return NULL;
+	}
 
 	if(len < 0 || len > maxlen)
 		len = maxlen;
--
libgit2 0.21.2