diff --git a/range-diff.c b/range-diff.c
index 767af8c..48b0e1b 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -460,7 +460,11 @@ int show_range_diff(const char *range1, const char *range2,
 		struct diff_options opts;
 		struct strbuf indent = STRBUF_INIT;
 
-		memcpy(&opts, diffopt, sizeof(opts));
+		if (diffopt)
+			memcpy(&opts, diffopt, sizeof(opts));
+		else
+			diff_setup(&opts);
+
 		if (!opts.output_format)
 			opts.output_format = DIFF_FORMAT_PATCH;
 		opts.flags.suppress_diff_headers = 1;