diff --git a/src/libiso8601/leap.c b/src/libiso8601/100_leap.c
similarity index 78%
rename from src/libiso8601/leap.c
rename to src/libiso8601/100_leap.c
index 4893473..cf2a900 100644
--- a/src/libiso8601/leap.c
+++ b/src/libiso8601/100_leap.c
@@ -1,4 +1,4 @@
-/* libiso8601/src/libiso8601/leap.c
+/* libiso8601/src/libiso8601/100_leap.c
  *
  *  (c)2006, Laurence Withers, <l@lwithers.me.uk>.
  *  Released under the GNU GPLv2. See file COPYING or
@@ -46,27 +46,6 @@ int iso8601_seconds_leap(const struct iso8601_date* date)
 
 
 
-int iso8601_valid_leap(const struct iso8601_date* date)
-{
-    int num_ly = 0, i = 0;
-
-    if(date->nsec < 0 || date->nsec >= BILLION) return 0;
-
-    switch(date->sec) {
-    case 0 ... 86399:
-        return 1;
-
-    case 86400: /* 23:59:60 */
-        num_ly = sizeof(leap_second_days) / sizeof(int);
-        for(i = 0; i < num_ly; ++i) if(leap_second_days[i] == date->day) return 1;
-        return 0;
-    }
-
-    return 0;
-}
-
-
-
 static int _leap_elapsed_day(int sday, int eday)
 {
     int spos, epos;
diff --git a/src/libiso8601/200_parser.c b/src/libiso8601/200_parser.c
index 7a51f1c..26b3caa 100644
--- a/src/libiso8601/200_parser.c
+++ b/src/libiso8601/200_parser.c
@@ -648,17 +648,17 @@ done:
         
     }
     
-    // correct for timezone offset (note trickery to end up at 23:59:60 iff a leap second was 
-    // requested)
+    /* correct for timezone offset (note trickery to end up at 23:59:60 iff a leap second was 
+     * requested), and ensure that any leap second requested was a valid leap second. */
     if(details) details->tz_sec = tz_sec;
     if(tz_sec && earliest) iso8601_add_seconds(earliest, - leap_sec_req - tz_sec);
     if(tz_sec && latest) iso8601_add_seconds(latest, - leap_sec_req - tz_sec);
-
-    // check that, if a leap second was requested, it was a valid leap second
     if(leap_sec_req) {
         ERROR_IF(earliest && earliest->sec != 86400);
         ERROR_IF(latest && latest->sec != 86400);
     }
+    ERROR_IF(earliest && iso8601_invalid(earliest));
+    ERROR_IF(latest && iso8601_invalid(latest));
 
     return 0;
 #undef ERROR_IF
@@ -667,6 +667,27 @@ done:
 
 
 
+int iso8601_invalid(const struct iso8601_date* date)
+{
+    int num_ly = 0, i = 0;
+
+    if(date->nsec < 0 || date->nsec >= BILLION) return 0;
+
+    switch(date->sec) {
+    case 0 ... 86399:
+        return 1;
+
+    case 86400: /* 23:59:60 */
+        num_ly = sizeof(leap_second_days) / sizeof(int);
+        for(i = 0; i < num_ly; ++i) if(leap_second_days[i] == date->day) return 1;
+        return 0;
+    }
+
+    return 0;
+}
+
+
+
 /* options for text editors
 kate: replace-trailing-space-save true; space-indent true; tab-width 4;
 vim: expandtab:ts=4:sw=4
diff --git a/src/libiso8601/200_parser.h b/src/libiso8601/200_parser.h
index bd5c762..e070b63 100644
--- a/src/libiso8601/200_parser.h
+++ b/src/libiso8601/200_parser.h
@@ -45,8 +45,12 @@ int iso8601_parse(const char* str, struct iso8601_date* earliest, struct iso8601
 \retval -1 if not valid.
 \retval 0 if valid.
 
+Checks the details of \a date to ensure that they are sensible. This involves checking that \a sec
+is in the range 0 to 86399 (or 86400 if there is a leap second), and that \a nsec is in the range 0
+to 999999999.
+
 */
-int iso8601_valid(const struct iso8601_date* date);
+int iso8601_invalid(const struct iso8601_date* date);
 
 
 
diff --git a/src/libiso8601/400_functions.h b/src/libiso8601/400_functions.h
index d1ca921..9e6b327 100644
--- a/src/libiso8601/400_functions.h
+++ b/src/libiso8601/400_functions.h
@@ -38,7 +38,6 @@ void iso8601_add_nanoseconds(struct iso8601_date* date, long nano);
 
 /* leap.c */
 int iso8601_seconds_leap(const struct iso8601_date* date);
-int iso8601_valid_leap(const struct iso8601_date* date);
 int iso8601_leap_elapsed(const struct iso8601_date* start, const struct iso8601_date* end);
 
 /* options for text editors