diff --git a/doc/fixes36.3 b/doc/fixes36.3
index 909dbd345..a20fc650e 100644
--- a/doc/fixes36.3
+++ b/doc/fixes36.3
@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.94 $ $NHDT-Date: 1562838835 2019/07/11 09:53:55 $
+$NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.95 $ $NHDT-Date: 1564269131 2019/07/27 23:12:11 $
 
 This fixes36.3 file is here to capture information about updates in the 3.6.x
 lineage following the release of 3.6.2 in May 2019. Please note, however,
@@ -105,6 +105,8 @@ when farlook describes a monster at a visible spot as trapped, reveal the trap
 fix theft when poly'd into nymph form; 3.6.2 change made that anger the victim
 hero poly'd into nymph would steal gold along with other items
 change wizard mode #panic to require "yes" if 'paranoid_confirm:quit' is set
+add some additional validation checks when setting up a new timer (triggered
+	by an ancient source comment rather than by any observed problems)
 
 
 Fixes to Post-3.6.2 Problems that Were Exposed Via git Repository
diff --git a/include/timeout.h b/include/timeout.h
index 0cb4c706a..0ac85a3c8 100644
--- a/include/timeout.h
+++ b/include/timeout.h
@@ -1,4 +1,4 @@
-/* NetHack 3.6	timeout.h	$NHDT-Date: 1432512775 2015/05/25 00:12:55 $  $NHDT-Branch: master $:$NHDT-Revision: 1.10 $ */
+/* NetHack 3.6	timeout.h	$NHDT-Date: 1564269131 2019/07/27 23:12:11 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.12 $ */
 /* Copyright 1994, Dean Luick					  */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -10,10 +10,11 @@ typedef void FDECL((*timeout_proc), (ANY_P *, long));
 
 /* kind of timer */
 enum timer_type {
-    TIMER_LEVEL = 0,   /* event specific to level */
-    TIMER_GLOBAL,  /* event follows current play */
-    TIMER_OBJECT,  /* event follows a object */
-    TIMER_MONSTER /* event follows a monster */
+    TIMER_LEVEL = 0,   /* event specific to level [melting ice] */
+    TIMER_GLOBAL = 1,  /* event follows current play [not used] */
+    TIMER_OBJECT = 2,  /* event follows an object [various] */
+    TIMER_MONSTER = 3, /* event follows a monster [not used] */
+    NUM_TIMER_KINDS    /* 4 */
 };
 
 /* save/restore timer ranges */
diff --git a/src/timeout.c b/src/timeout.c
index 54a2943c3..3d820b0fb 100644
--- a/src/timeout.c
+++ b/src/timeout.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6	timeout.c	$NHDT-Date: 1559664953 2019/06/04 16:15:53 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.90 $ */
+/* NetHack 3.6	timeout.c	$NHDT-Date: 1564269133 2019/07/27 23:12:13 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.91 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2018. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -1868,13 +1868,32 @@ short kind;
 short func_index;
 anything *arg;
 {
-    timer_element *gnu;
+    timer_element *gnu, *dup;
 
-    if (func_index < 0 || func_index >= NUM_TIME_FUNCS)
-        panic("start_timer");
+    if (kind < 0 || kind >= NUM_TIMER_KINDS
+        || func_index < 0 || func_index >= NUM_TIME_FUNCS)
+        panic("start_timer (%s: %d)", kind_name(kind), (int) func_index);
 
-    gnu = (timer_element *) alloc(sizeof(timer_element));
-    (void) memset((genericptr_t)gnu, 0, sizeof(timer_element));
+    /* fail if <arg> already has a <func_index> timer running */
+    for (dup = timer_base; dup; dup = dup->next)
+        if (dup->kind == kind
+            && dup->func_index == func_index
+            && dup->arg.a_void == arg->a_void)
+            break;
+    if (dup) {
+        char idbuf[QBUFSZ];
+
+#ifdef VERBOSE_TIMER
+        Sprintf(idbuf, "%s timer", timeout_funcs[func_index].name);
+#else
+        Sprintf(idbuf, "%s timer (%d)", kind_name(kind), (int) func_index);
+#endif
+        impossible("Attempted to start duplicate %s, aborted.", idbuf);
+        return FALSE;
+    }
+
+    gnu = (timer_element *) alloc(sizeof *gnu);
+    (void) memset((genericptr_t) gnu, 0, sizeof *gnu);
     gnu->next = 0;
     gnu->tid = timer_id++;
     gnu->timeout = monstermoves + when;
@@ -1887,7 +1906,6 @@ anything *arg;
     if (kind == TIMER_OBJECT) /* increment object's timed count */
         (arg->a_obj)->timed++;
 
-    /* should check for duplicates and fail if any */
     return TRUE;
 }