Index: funcs/func_env.c
===================================================================
--- funcs/func_env.c	(revision 390821)
+++ funcs/func_env.c	(working copy)
@@ -541,7 +541,7 @@
 
 			/* Don't go past the length requested */
 			if (off_i + toappend > offset + length) {
-				toappend = length - off_i;
+				toappend = offset + length - off_i;
 			}
 
 			ast_str_append_substr(buf, len, fbuf, toappend);