Index: generic/tclClock.c
==================================================================
--- generic/tclClock.c
+++ generic/tclClock.c
@@ -3739,12 +3739,12 @@
 	    Tcl_SetErrorCode(opts->interp, "CLOCK", "dateTooLarge", (char *)NULL);
 	    return TCL_ERROR;
 	}
     }
 
-    /* If seconds overflows the day (no validate case), increase days */
-    if (yySecondOfDay >= SECONDS_PER_DAY) {
+    /* If seconds overflows the day (no validate and "24:00" case), increase days */
+    if (yySecondOfDay >= SECONDS_PER_DAY + ((info->flags & CLF_TIME) && (yyHour == 24))) {
 	yydate.julianDay += (yySecondOfDay / SECONDS_PER_DAY);
 	yySecondOfDay %= SECONDS_PER_DAY;
     }
 
     /* Local seconds to UTC (stored in yydate.seconds) */
@@ -3884,23 +3884,23 @@
 	}
     }
 
     if (info->flags & CLF_TIME) {
 	/* hour */
-	if (yyHour < 0 || yyHour > ((yyMeridian == MER24) ? 23 : 12)) {
+	if (yyHour < 0 || yyHour > ((yyMeridian == MER24) ? 24 : 12)) {
 	    errMsg = "invalid time (hour)";
 	    errCode = "hour";
 	    goto error;
 	}
 	/* minutes */
-	if (yyMinutes < 0 || yyMinutes > 59) {
+	if (yyMinutes < 0 || yyMinutes > 59 || (yyMinutes && (yyHour == 24))) {
 	    errMsg = "invalid time (minutes)";
 	    errCode = "minutes";
 	    goto error;
 	}
 	/* oldscan could return secondOfDay (parsedTime) -1 by invalid time (ex.: 25:00:00) */
-	if (yySeconds < 0 || yySeconds > 59 || yySecondOfDay <= -1) {
+	if (yySeconds < 0 || yySeconds > 59 || yySecondOfDay <= -1 || (yySeconds && (yyHour == 24))) {
 	    errMsg = "invalid time";
 	    errCode = "seconds";
 	    goto error;
 	}
     }

Index: generic/tclDate.c
==================================================================
--- generic/tclDate.c
+++ generic/tclDate.c
@@ -2346,13 +2346,13 @@
 {
     switch (Meridian) {
     case MER24:
 	return (Hours * 60 + Minutes) * 60 + Seconds;
     case MERam:
-	return ((Hours % 12) * 60 + Minutes) * 60 + Seconds;
+	return (((Hours / 24) * 24 + (Hours % 12)) * 60 + Minutes) * 60 + Seconds;
     case MERpm:
-	return (((Hours % 12) + 12) * 60 + Minutes) * 60 + Seconds;
+	return (((Hours / 24) * 24 + (Hours % 12) + 12) * 60 + Minutes) * 60 + Seconds;
     }
     return -1;			/* Should never be reached */
 }
 
 static int

Index: generic/tclGetDate.y
==================================================================
--- generic/tclGetDate.y
+++ generic/tclGetDate.y
@@ -716,13 +716,13 @@
 {
     switch (Meridian) {
     case MER24:
 	return (Hours * 60 + Minutes) * 60 + Seconds;
     case MERam:
-	return ((Hours % 12) * 60 + Minutes) * 60 + Seconds;
+	return (((Hours / 24) * 24 + (Hours % 12)) * 60 + Minutes) * 60 + Seconds;
     case MERpm:
-	return (((Hours % 12) + 12) * 60 + Minutes) * 60 + Seconds;
+	return (((Hours / 24) * 24 + (Hours % 12) + 12) * 60 + Minutes) * 60 + Seconds;
     }
     return -1;			/* Should never be reached */
 }
 
 static int

Index: tests/clock.test
==================================================================
--- tests/clock.test
+++ tests/clock.test
@@ -37179,17 +37179,17 @@
 	 [clock scan 24:00:00 -base 0 -gmt 1] \
 	 [clock scan 48:00:00 -base 0 -gmt 1]
   } {86399 86400 172800}
 } else {
   test clock-46.8a {regression test - invalid time (hour)} {
-    list [catch {clock scan 24:00:00 -base 0 -gmt 1 -format %H:%M:%S} msg] $msg \
+    list [catch {clock scan 24:00:01 -base 0 -gmt 1 -format %H:%M:%S} msg] $msg \
 	 [catch {clock scan 48:00:00 -base 0 -gmt 1 -format %H:%M:%S} msg] $msg
-  } {1 {unable to convert input string: invalid time (hour)} 1 {unable to convert input string: invalid time (hour)}}
+  } {1 {unable to convert input string: invalid time} 1 {unable to convert input string: invalid time (hour)}}
   test clock-46.8b {freescan: regression test - invalid time (hour)} {
-    list [catch {clock scan 24:00:00 -base 0 -gmt 1} msg] $msg \
+    list [catch {clock scan 24:00:01 -base 0 -gmt 1} msg] $msg \
 	 [catch {clock scan 48:00:00 -base 0 -gmt 1} msg] $msg
-  } {1 {unable to convert input string: invalid time (hour)} 1 {unable to convert input string: invalid time (hour)}}
+  } {1 {unable to convert input string: invalid time} 1 {unable to convert input string: invalid time (hour)}}
 }
 
 proc _invalid_test {testtz scnargs args} {
     global valid_mode
     # ensure validation works TZ independently, since the conversion
@@ -38467,12 +38467,12 @@
     set res {}
     foreach {d i} {
 	"2012-06-29 23:59:60" "invalid time"
 	"2012-05-30 23:59:60" "invalid time"
 	"2012-05-30 23:60:60" "invalid time"
-	"2012-05-30 24:00:60" "invalid time"
-	"2012-05-30 24:60:00" "invalid time"
+	"2012-05-30 24:00:01" "invalid time"
+	"2012-05-30 24:10:00" "invalid time"
     } {
 	# check with free scan:
 	if {![catch { clock scan $d -gmt 1 } t] || ![string match *$i* $t]} {
 	    lappend res "free-scan \"$d\" == \"$t\", expected \"$i\""
 	}