diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index 3f86737..ae8f621 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -390,6 +390,15 @@
 	}
 }
 
+static struct data__file *fmt_to_data_file(struct perf_hpp_fmt *fmt)
+{
+	struct diff_hpp_fmt *dfmt = container_of(fmt, struct diff_hpp_fmt, fmt);
+	void *ptr = dfmt - dfmt->idx;
+	struct data__file *d = container_of(ptr, struct data__file, fmt);
+
+	return d;
+}
+
 static struct hist_entry*
 get_pair_data(struct hist_entry *he, struct data__file *d)
 {
@@ -407,8 +416,7 @@
 static struct hist_entry*
 get_pair_fmt(struct hist_entry *he, struct diff_hpp_fmt *dfmt)
 {
-	void *ptr = dfmt - dfmt->idx;
-	struct data__file *d = container_of(ptr, struct data__file, fmt);
+	struct data__file *d = fmt_to_data_file(&dfmt->fmt);
 
 	return get_pair_data(he, d);
 }