diff --git a/src/libiso8601/400_manip.c b/src/libiso8601/400_manip.c
index f766b18..c6ce9a8 100644
--- a/src/libiso8601/400_manip.c
+++ b/src/libiso8601/400_manip.c
@@ -38,6 +38,19 @@ int iso8601_eq(const struct iso8601_date* d1, const struct iso8601_date* d2)
 
 
 
+int iso8601_cmp(const struct iso8601_date* d1, const struct iso8601_date* d2)
+{
+    if(d1->day < d2->day) return -1;
+    if(d1->day > d2->day) return 1;
+    if(d1->sec < d2->sec) return -1;
+    if(d1->sec > d2->sec) return 1;
+    if(d1->nsec < d2->nsec) return -1;
+    if(d1->nsec > d2->nsec) return 1;
+    return 0;
+}
+
+
+
 void iso8601_add_elapsed(struct iso8601_date* date, const struct iso8601_elapsed* per)
 {
     div_t qr;
diff --git a/src/libiso8601/400_manip.h b/src/libiso8601/400_manip.h
index c8d69dc..dd80360 100644
--- a/src/libiso8601/400_manip.h
+++ b/src/libiso8601/400_manip.h
@@ -53,6 +53,19 @@ int iso8601_eq(const struct iso8601_date* d1, const struct iso8601_date* d2);
 
 
 
+/*! \brief Comparison (for qsort et al.).
+
+\param d1 First date to compare.
+\param d2 Second date to compare.
+\retval -1 if \a d1 &lt; \a d2
+\retval 0 if \a d1 == \a d2
+\retval 1 if \a d1 &gt; \a d2
+
+*/
+int iso8601_cmp(const struct iso8601_date* d1, const struct iso8601_date* d2);
+
+
+
 /*! \brief Add a period to a date.
 
 \param[in,out] date Date to modify.