diff --git a/cache.h b/cache.h
index 107ac61b68..dd9e689daf 100644
--- a/cache.h
+++ b/cache.h
@@ -1045,6 +1045,13 @@ struct ident_split {
  */
 extern int split_ident_line(struct ident_split *, const char *, int);
 
+/*
+ * Like show_date, but pull the timestamp and tz parameters from
+ * the ident_split. It will also sanity-check the values and produce
+ * a well-known sentinel date if they appear bogus.
+ */
+const char *show_ident_date(const struct ident_split *id, enum date_mode mode);
+
 /*
  * Compare split idents for equality or strict ordering. Note that we
  * compare only the ident part of the line, ignoring any timestamp.
diff --git a/pretty.c b/pretty.c
index 3c43db558a..e1e2cad36d 100644
--- a/pretty.c
+++ b/pretty.c
@@ -393,8 +393,8 @@ static void add_rfc2047(struct strbuf *sb, const char *line, size_t len,
 	strbuf_addstr(sb, "?=");
 }
 
-static const char *show_ident_date(const struct ident_split *ident,
-				   enum date_mode mode)
+const char *show_ident_date(const struct ident_split *ident,
+			    enum date_mode mode)
 {
 	unsigned long date = 0;
 	long tz = 0;