diff --git a/notiming.c b/notiming.c
index 384fa670..5fe44038 100644
--- a/notiming.c
+++ b/notiming.c
@@ -11,7 +11,7 @@
 
 #include "putty.h"
 
-long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
+unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
 {
     return 0;
 }
diff --git a/pinger.c b/pinger.c
index 3e2626f5..3f533ae6 100644
--- a/pinger.c
+++ b/pinger.c
@@ -8,18 +8,18 @@
 struct pinger_tag {
     int interval;
     int pending;
-    long next;
+    unsigned long next;
     Backend *back;
     void *backhandle;
 };
 
 static void pinger_schedule(Pinger pinger);
 
-static void pinger_timer(void *ctx, long now)
+static void pinger_timer(void *ctx, unsigned long now)
 {
     Pinger pinger = (Pinger)ctx;
 
-    if (pinger->pending && now - pinger->next >= 0) {
+    if (pinger->pending && now == pinger->next) {
 	pinger->back->special(pinger->backhandle, TS_PING);
 	pinger->pending = FALSE;
 	pinger_schedule(pinger);
diff --git a/putty.h b/putty.h
index bc400fb2..6534da74 100644
--- a/putty.h
+++ b/putty.h
@@ -1383,11 +1383,11 @@ char *get_random_data(int bytes);      /* used in cmdgen.c */
  * GETTICKCOUNT() and compare the result with the returned `next'
  * value to find out how long you have to make your next wait().)
  */
-typedef void (*timer_fn_t)(void *ctx, long now);
-long schedule_timer(int ticks, timer_fn_t fn, void *ctx);
+typedef void (*timer_fn_t)(void *ctx, unsigned long now);
+unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx);
 void expire_timer_context(void *ctx);
-int run_timers(long now, long *next);
-void timer_change_notify(long next);
+int run_timers(unsigned long now, unsigned long *next);
+void timer_change_notify(unsigned long next);
 
 /*
  * Define no-op macros for the jump list functions, on platforms that
diff --git a/ssh.c b/ssh.c
index 4bbb30bd..1cbb4715 100644
--- a/ssh.c
+++ b/ssh.c
@@ -772,7 +772,7 @@ static int ssh_do_close(Ssh ssh, int notify_exit);
 static unsigned long ssh_pkt_getuint32(struct Packet *pkt);
 static int ssh2_pkt_getbool(struct Packet *pkt);
 static void ssh_pkt_getstring(struct Packet *pkt, char **p, int *length);
-static void ssh2_timer(void *ctx, long now);
+static void ssh2_timer(void *ctx, unsigned long now);
 static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 			      struct Packet *pktin);
 static void ssh2_msg_unexpected(Ssh ssh, struct Packet *pktin);
@@ -981,7 +981,7 @@ struct ssh_tag {
     unsigned long incoming_data_size, outgoing_data_size, deferred_data_size;
     unsigned long max_data_size;
     int kex_in_progress;
-    long next_rekey, last_rekey;
+    unsigned long next_rekey, last_rekey;
     char *deferred_rekey_reason;    /* points to STATIC string; don't free */
 
     /*
@@ -9482,7 +9482,7 @@ static void ssh2_protocol_setup(Ssh ssh)
     ssh->packet_dispatch[SSH2_MSG_DEBUG] = ssh2_msg_debug;
 }
 
-static void ssh2_timer(void *ctx, long now)
+static void ssh2_timer(void *ctx, unsigned long now)
 {
     Ssh ssh = (Ssh)ctx;
 
@@ -9490,7 +9490,7 @@ static void ssh2_timer(void *ctx, long now)
 	return;
 
     if (!ssh->kex_in_progress && conf_get_int(ssh->conf, CONF_ssh_rekey_time) != 0 &&
-	now - ssh->next_rekey >= 0) {
+	now == ssh->next_rekey) {
 	do_ssh2_transport(ssh, "timeout", -1, NULL);
     }
 }
@@ -9773,10 +9773,10 @@ static void ssh_reconfig(void *handle, Conf *conf)
     rekey_time = conf_get_int(conf, CONF_ssh_rekey_time);
     if (conf_get_int(ssh->conf, CONF_ssh_rekey_time) != rekey_time &&
 	rekey_time != 0) {
-	long new_next = ssh->last_rekey + rekey_time*60*TICKSPERSEC;
-	long now = GETTICKCOUNT();
+	unsigned long new_next = ssh->last_rekey + rekey_time*60*TICKSPERSEC;
+	unsigned long now = GETTICKCOUNT();
 
-	if (new_next - now < 0) {
+	if (now - ssh->last_rekey > rekey_time*60*TICKSPERSEC) {
 	    rekeying = "timeout shortened";
 	} else {
 	    ssh->next_rekey = schedule_timer(new_next - now, ssh2_timer, ssh);
diff --git a/sshrand.c b/sshrand.c
index b728fd95..4c33f4a0 100644
--- a/sshrand.c
+++ b/sshrand.c
@@ -199,9 +199,9 @@ static void random_add_heavynoise_bitbybit(void *noise, int length)
     pool.poolpos = i;
 }
 
-static void random_timer(void *ctx, long now)
+static void random_timer(void *ctx, unsigned long now)
 {
-    if (random_active > 0 && now - next_noise_collection >= 0) {
+    if (random_active > 0 && now == next_noise_collection) {
 	noise_regular();
 	next_noise_collection =
 	    schedule_timer(NOISE_REGULAR_INTERVAL, random_timer, &pool);
diff --git a/terminal.c b/terminal.c
index cc4b0d8f..72bfbc9b 100644
--- a/terminal.c
+++ b/terminal.c
@@ -1065,32 +1065,32 @@ static termline *lineptr(Terminal *term, int y, int lineno, int screen)
 static void term_schedule_tblink(Terminal *term);
 static void term_schedule_cblink(Terminal *term);
 
-static void term_timer(void *ctx, long now)
+static void term_timer(void *ctx, unsigned long now)
 {
     Terminal *term = (Terminal *)ctx;
     int update = FALSE;
 
-    if (term->tblink_pending && now - term->next_tblink >= 0) {
+    if (term->tblink_pending && now == term->next_tblink) {
 	term->tblinker = !term->tblinker;
 	term->tblink_pending = FALSE;
 	term_schedule_tblink(term);
 	update = TRUE;
     }
 
-    if (term->cblink_pending && now - term->next_cblink >= 0) {
+    if (term->cblink_pending && now == term->next_cblink) {
 	term->cblinker = !term->cblinker;
 	term->cblink_pending = FALSE;
 	term_schedule_cblink(term);
 	update = TRUE;
     }
 
-    if (term->in_vbell && now - term->vbell_end >= 0) {
+    if (term->in_vbell && now == term->vbell_end) {
 	term->in_vbell = FALSE;
 	update = TRUE;
     }
 
     if (update ||
-	(term->window_update_pending && now - term->next_update >= 0))
+	(term->window_update_pending && now == term->next_update))
 	term_update(term);
 }
 
diff --git a/timing.c b/timing.c
index ffea4e14..11a03050 100644
--- a/timing.c
+++ b/timing.c
@@ -36,13 +36,13 @@
 struct timer {
     timer_fn_t fn;
     void *ctx;
-    long now;
-    long when_set;
+    unsigned long now;
+    unsigned long when_set;
 };
 
 static tree234 *timers = NULL;
 static tree234 *timer_contexts = NULL;
-static long now = 0L;
+static unsigned long now = 0L;
 
 static int compare_timers(void *av, void *bv)
 {
@@ -106,9 +106,9 @@ static void init_timers(void)
     }
 }
 
-long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
+unsigned long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
 {
-    long when;
+    unsigned long when;
     struct timer *t, *first;
 
     init_timers();
@@ -153,7 +153,7 @@ long schedule_timer(int ticks, timer_fn_t fn, void *ctx)
  * Returns the time (in ticks) expected until the next timer after
  * that triggers.
  */
-int run_timers(long anow, long *next)
+int run_timers(unsigned long anow, unsigned long *next)
 {
     struct timer *first;
 
@@ -174,8 +174,8 @@ int run_timers(long anow, long *next)
 	     */
 	    delpos234(timers, 0);
 	    sfree(first);
-	} else if (first->now - now <= 0 ||
-	           now - (first->when_set - 10) < 0) {
+	} else if (now - first->when_set - 10 >
+		   first->now - first->when_set - 10) {
 	    /*
 	     * This timer is active and has reached its running
 	     * time. Run it.
diff --git a/unix/gtkwin.c b/unix/gtkwin.c
index 241aa6bc..2c0df9cb 100644
--- a/unix/gtkwin.c
+++ b/unix/gtkwin.c
@@ -1400,13 +1400,18 @@ void notify_remote_exit(void *frontend)
 
 static gint timer_trigger(gpointer data)
 {
-    long now = GPOINTER_TO_LONG(data);
-    long next;
+    unsigned long now = GPOINTER_TO_LONG(data);
+    unsigned long next, then;
     long ticks;
 
     if (run_timers(now, &next)) {
-	ticks = next - GETTICKCOUNT();
-	timer_id = gtk_timeout_add(ticks > 0 ? ticks : 1, timer_trigger,
+	then = now;
+	now = GETTICKCOUNT();
+	if (now - then > next - then)
+	    ticks = 0;
+	else
+	    ticks = next - now;
+	timer_id = gtk_timeout_add(ticks, timer_trigger,
 				   LONG_TO_GPOINTER(next));
     }
 
@@ -1417,7 +1422,7 @@ static gint timer_trigger(gpointer data)
     return FALSE;
 }
 
-void timer_change_notify(long next)
+void timer_change_notify(unsigned long next)
 {
     long ticks;
 
diff --git a/unix/uxcons.c b/unix/uxcons.c
index 73126c02..882d2c9b 100644
--- a/unix/uxcons.c
+++ b/unix/uxcons.c
@@ -70,7 +70,7 @@ void notify_remote_exit(void *frontend)
 {
 }
 
-void timer_change_notify(long next)
+void timer_change_notify(unsigned long next)
 {
 }
 
diff --git a/unix/uxplink.c b/unix/uxplink.c
index 61b9426b..0d896225 100644
--- a/unix/uxplink.c
+++ b/unix/uxplink.c
@@ -593,7 +593,7 @@ int main(int argc, char **argv)
     int errors;
     int use_subsystem = 0;
     int got_host = FALSE;
-    long now;
+    unsigned long now;
     struct winsize size;
 
     fdlist = NULL;
@@ -1016,12 +1016,17 @@ int main(int argc, char **argv)
 	}
 
 	do {
-	    long next, ticks;
+	    unsigned long next, then;
+	    long ticks;
 	    struct timeval tv, *ptv;
 
 	    if (run_timers(now, &next)) {
-		ticks = next - GETTICKCOUNT();
-		if (ticks < 0) ticks = 0;   /* just in case */
+		then = now;
+		now = GETTICKCOUNT();
+		if (now - then > next - then)
+		    ticks = 0;
+		else
+		    ticks = next - now;
 		tv.tv_sec = ticks / 1000;
 		tv.tv_usec = ticks % 1000 * 1000;
 		ptv = &tv;
diff --git a/unix/uxsftp.c b/unix/uxsftp.c
index a92cfc9d..f68685a0 100644
--- a/unix/uxsftp.c
+++ b/unix/uxsftp.c
@@ -443,7 +443,7 @@ static int ssh_sftp_do_select(int include_stdin, int no_fds_ok)
     fd_set rset, wset, xset;
     int i, fdcount, fdsize, *fdlist;
     int fd, fdstate, rwx, ret, maxfd;
-    long now = GETTICKCOUNT();
+    unsigned long now = GETTICKCOUNT();
 
     fdlist = NULL;
     fdcount = fdsize = 0;
@@ -489,13 +489,17 @@ static int ssh_sftp_do_select(int include_stdin, int no_fds_ok)
 	    FD_SET_MAX(0, maxfd, rset);
 
 	do {
-	    long next, ticks;
+	    unsigned long next, then;
+	    long ticks;
 	    struct timeval tv, *ptv;
 
 	    if (run_timers(now, &next)) {
-		ticks = next - GETTICKCOUNT();
-		if (ticks <= 0)
-		    ticks = 1;	       /* just in case */
+		then = now;
+		now = GETTICKCOUNT();
+		if (now - then > next - then)
+		    ticks = 0;
+		else
+		    ticks = next - now;
 		tv.tv_sec = ticks / 1000;
 		tv.tv_usec = ticks % 1000 * 1000;
 		ptv = &tv;
diff --git a/windows/wincons.c b/windows/wincons.c
index 9824a5a5..508be3f8 100644
--- a/windows/wincons.c
+++ b/windows/wincons.c
@@ -41,7 +41,7 @@ void notify_remote_exit(void *frontend)
 {
 }
 
-void timer_change_notify(long next)
+void timer_change_notify(unsigned long next)
 {
 }
 
diff --git a/windows/window.c b/windows/window.c
index d970dd19..5fe21787 100644
--- a/windows/window.c
+++ b/windows/window.c
@@ -2012,10 +2012,14 @@ void notify_remote_exit(void *fe)
     }
 }
 
-void timer_change_notify(long next)
+void timer_change_notify(unsigned long next)
 {
-    long ticks = next - GETTICKCOUNT();
-    if (ticks <= 0) ticks = 1;	       /* just in case */
+    unsigned long now = GETTICKCOUNT();
+    long ticks;
+    if (now - next < INT_MAX)
+	ticks = 0;
+    else
+	ticks = next - now;
     KillTimer(hwnd, TIMING_TIMER_ID);
     SetTimer(hwnd, TIMING_TIMER_ID, ticks, NULL);
     timing_next_time = next;
@@ -2042,7 +2046,7 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
     switch (message) {
       case WM_TIMER:
 	if ((UINT_PTR)wParam == TIMING_TIMER_ID) {
-	    long next;
+	    unsigned long next;
 
 	    KillTimer(hwnd, TIMING_TIMER_ID);
 	    if (run_timers(timing_next_time, &next)) {
@@ -5354,9 +5358,9 @@ static int flashing = 0;
  * Timer for platforms where we must maintain window flashing manually
  * (e.g., Win95).
  */
-static void flash_window_timer(void *ctx, long now)
+static void flash_window_timer(void *ctx, unsigned long now)
 {
-    if (flashing && now - next_flash >= 0) {
+    if (flashing && now == next_flash) {
 	flash_window(1);
     }
 }
diff --git a/windows/winplink.c b/windows/winplink.c
index 58063352..7ec98e7f 100644
--- a/windows/winplink.c
+++ b/windows/winplink.c
@@ -289,7 +289,7 @@ int main(int argc, char **argv)
     int errors;
     int got_host = FALSE;
     int use_subsystem = 0;
-    long now, next;
+    unsigned long now, next, then;
 
     sklist = NULL;
     skcount = sksize = 0;
@@ -634,8 +634,12 @@ int main(int argc, char **argv)
 	}
 
 	if (run_timers(now, &next)) {
-	    ticks = next - GETTICKCOUNT();
-	    if (ticks < 0) ticks = 0;  /* just in case */
+	then = now;
+	now = GETTICKCOUNT();
+	if (now - then > next - then)
+	    ticks = 0;
+	else
+	    ticks = next - now;
 	} else {
 	    ticks = INFINITE;
 	}
diff --git a/windows/winser.c b/windows/winser.c
index e0fc20e7..086d3e5c 100644
--- a/windows/winser.c
+++ b/windows/winser.c
@@ -331,11 +331,11 @@ static void serial_size(void *handle, int width, int height)
     return;
 }
 
-static void serbreak_timer(void *ctx, long now)
+static void serbreak_timer(void *ctx, unsigned long now)
 {
     Serial serial = (Serial)ctx;
 
-    if (now >= serial->clearbreak_time && serial->port) {
+    if (now == serial->clearbreak_time && serial->port) {
 	ClearCommBreak(serial->port);
 	serial->break_in_progress = FALSE;
 	logevent(serial->frontend, "Finished serial break");
diff --git a/windows/winsftp.c b/windows/winsftp.c
index e6b55c1d..d4c5fa6e 100644
--- a/windows/winsftp.c
+++ b/windows/winsftp.c
@@ -486,15 +486,20 @@ extern int select_result(WPARAM, LPARAM);
 int do_eventsel_loop(HANDLE other_event)
 {
     int n, nhandles, nallhandles, netindex, otherindex;
-    long next, ticks;
+    unsigned long next, then;
+    long ticks;
     HANDLE *handles;
     SOCKET *sklist;
     int skcount;
-    long now = GETTICKCOUNT();
+    unsigned long now = GETTICKCOUNT();
 
     if (run_timers(now, &next)) {
-	ticks = next - GETTICKCOUNT();
-	if (ticks < 0) ticks = 0;  /* just in case */
+	then = now;
+	now = GETTICKCOUNT();
+	if (now - then > next - then)
+	    ticks = 0;
+	else
+	    ticks = next - now;
     } else {
 	ticks = INFINITE;
     }