diff --git a/man/remind.1.in b/man/remind.1.in
index f37a7c91..f6644780 100644
--- a/man/remind.1.in
+++ b/man/remind.1.in
@@ -3467,8 +3467,10 @@ This function takes a \fBDATE\fR or \fBDATETIME\fR as an argument, and
 returns an \fBINT\fR that is the day-of-month component of
 \fIdate\fR.
 .TP
-.B daysinmon(i_m, i_y)
+.B daysinmon(i_m, i_y)\fR or \fB daysinmon(dq_date)\fR
 Returns the number of days in month \fIm\fR (1-12) of the year \fIy\fR.
+If given a DATE or DATETIME argument, returns the number of days in
+the month containing the argument.
 .TP
 .B defined(s_var)
 Returns 1 if the variable named by \fIvar\fR is defined, or 0 if it is not.
diff --git a/src/funcs.c b/src/funcs.c
index d271cd26..db989348 100644
--- a/src/funcs.c
+++ b/src/funcs.c
@@ -267,7 +267,7 @@ BuiltinFunc Func[] = {
     {   "datetime",     2,      5,      1,          FDateTime, NULL },
     {   "dawn",         0,      1,      0,          FDawn, NULL },
     {   "day",          1,      1,      1,          FDay, NULL },
-    {   "daysinmon",    2,      2,      1,          FDaysinmon, NULL },
+    {   "daysinmon",    1,      2,      1,          FDaysinmon, NULL },
     {   "defined",      1,      1,      0,          FDefined, NULL },
     {   "dosubst",      1,      3,      0,          FDosubst, NULL },
     {   "dusk",         0,      1,      0,          FDusk, NULL },
@@ -2008,19 +2008,30 @@ static int FTrigdatetime(func_info *info)
 /*                                                             */
 /*  FDaysinmon                                                 */
 /*                                                             */
-/*  Returns the number of days in mon,yr                       */
+/*  Returns the number of days in mon,yr OR month containing   */
+/*  given date.                                                */
 /*                                                             */
 /***************************************************************/
 static int FDaysinmon(func_info *info)
 {
-    if (ARG(0).type != INT_TYPE || ARG(1).type != INT_TYPE) return E_BAD_TYPE;
+    int y, m;
 
-    if (ARGV(0) > 12 || ARGV(0) < 1 ||
-        ARGV(1) < BASE || ARGV(1) > BASE+YR_RANGE)
-        return E_DOMAIN_ERR;
+    if (Nargs == 1) {
+        if (!HASDATE(ARG(0))) return E_BAD_TYPE;
+        FromDSE(DATEPART(ARG(0)), &y, &m, NULL);
+    } else {
+        if (ARG(0).type != INT_TYPE || ARG(1).type != INT_TYPE) return E_BAD_TYPE;
+
+        if (ARGV(0) > 12 || ARGV(0) < 1 ||
+            ARGV(1) < BASE || ARGV(1) > BASE+YR_RANGE) {
+            return E_DOMAIN_ERR;
+        }
+        m = ARGV(0) - 1;
+        y = ARGV(1);
+    }
 
     RetVal.type = INT_TYPE;
-    RETVAL = DaysInMonth(ARGV(0)-1, ARGV(1));
+    RETVAL = DaysInMonth(m, y);
     return OK;
 }
 
diff --git a/tests/test.cmp b/tests/test.cmp
index e46c2989..ffdf6800 100644
--- a/tests/test.cmp
+++ b/tests/test.cmp
@@ -16579,6 +16579,14 @@ Base: 1991-02-09
 ../tests/test.rem(1612): Expired
 trigvalid = 1; trigdate = 1991-01-14
 trigvalid = 0; trigdate = 0
+daysinmon(2, 2000) => 29
+daysinmon(2, 2001) => 28
+daysinmon(3, 2000) => 31
+daysinmon(3, 2001) => 31
+daysinmon(2000-02-14) => 29
+daysinmon(2001-02-14) => 28
+daysinmon(2000-04-14) => 30
+daysinmon(2001-04-14) => 30
 Variable hash table statistics:
   Entries: 100143; Buckets: 87719; Non-empty Buckets: 66301
   Maxlen: 5; Minlen: 0; Avglen: 1.142; Stddev: 0.878; Avg nonempty len: 1.510
diff --git a/tests/test.rem b/tests/test.rem
index 1164d1f3..0993f0e2 100644
--- a/tests/test.rem
+++ b/tests/test.rem
@@ -1626,6 +1626,18 @@ set b trigdate()
 
 REM MSG trigvalid = [a]; trigdate = [b]
 
+DEBUG +x
+set a daysinmon(2, 2000)
+set a daysinmon(2, 2001)
+set a daysinmon(3, 2000)
+set a daysinmon(3, 2001)
+
+set a daysinmon('2000-02-14')
+set a daysinmon('2001-02-14')
+set a daysinmon('2000-04-14')
+set a daysinmon('2001-04-14')
+
+DEBUG -x
 # Output expression-node stats
 DEBUG +h