usage_with_options(merge_file_usage, options);
        if (quiet) {
                if (!freopen("/dev/null", "w", stderr))
-                       return error("failed to redirect stderr to /dev/null: "
-                                    "%s", strerror(errno));
+                       return error_errno("failed to redirect stderr to /dev/null");
        }
 
        if (prefix)
                        names[i] = argv[i];
                if (read_mmfile(mmfs + i, fname))
                        return -1;
-               if (buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
+               if (mmfs[i].size > MAX_XDIFF_SIZE ||
+                   buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
                        return error("Cannot merge binary files: %s",
                                        argv[i]);
        }
                FILE *f = to_stdout ? stdout : fopen(fpath, "wb");
 
                if (!f)
-                       ret = error("Could not open %s for writing", filename);
+                       ret = error_errno("Could not open %s for writing",
+                                         filename);
                else if (result.size &&
                         fwrite(result.ptr, result.size, 1, f) != 1)
-                       ret = error("Could not write to %s", filename);
+                       ret = error_errno("Could not write to %s", filename);
                else if (fclose(f))
-                       ret = error("Could not close %s", filename);
+                       ret = error_errno("Could not close %s", filename);
                free(result.ptr);
        }
 
+       if (ret > 127)
+               ret = 127;
+
        return ret;
 }