diff --git a/src/include/utils/timestamp.h b/src/include/utils/timestamp.h
index 2fc52d5b569..ae2ef56e0ea 100644
--- a/src/include/utils/timestamp.h
+++ b/src/include/utils/timestamp.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/timestamp.h,v 1.48 2005/07/21 03:56:24 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/timestamp.h,v 1.49 2005/07/21 04:48:42 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -61,13 +61,12 @@ typedef struct
 #define MAX_INTERVAL_PRECISION 6
 
 /* in both timestamp.h and ecpg/dt.h */
-#define DAYS_PER_YEAR	365.25
+#define DAYS_PER_YEAR	365.25	/* assumes leap year every four years */
 #define MONTHS_PER_YEAR	12
-/* average days per month */
-#define DAYS_PER_MONTH	30
-#define HOURS_PER_DAY	24
+#define DAYS_PER_MONTH	30		/* assumes exactly 30 days per month */
+#define HOURS_PER_DAY	24		/* assume no daylight savings time changes */
 
-#define SECS_PER_DAY	86400
+#define SECS_PER_DAY	86400	/* assumes no leap second */
 #define SECS_PER_HOUR   3600
 #define SECS_PER_MINUTE 60
 
diff --git a/src/interfaces/ecpg/pgtypeslib/dt.h b/src/interfaces/ecpg/pgtypeslib/dt.h
index cda88000456..14fbd3c9878 100644
--- a/src/interfaces/ecpg/pgtypeslib/dt.h
+++ b/src/interfaces/ecpg/pgtypeslib/dt.h
@@ -217,13 +217,12 @@ do { \
 #endif
 
 /* in both timestamp.h and ecpg/dt.h */
-#define DAYS_PER_YEAR	365.25
+#define DAYS_PER_YEAR	365.25	/* assumes leap year every four years */
 #define MONTHS_PER_YEAR	12
-/* average days per month */
-#define DAYS_PER_MONTH	30
-#define HOURS_PER_DAY	24
+#define DAYS_PER_MONTH	30		/* assumes exactly 30 days per month */
+#define HOURS_PER_DAY	24		/* assume no daylight savings time changes */
 
-#define SECS_PER_DAY	86400
+#define SECS_PER_DAY	86400	/* assumes no leap second */
 #define SECS_PER_HOUR   3600
 #define SECS_PER_MINUTE 60