diff --git a/README.md b/README.md
index 75e5115..7f5d266 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,8 @@ Refer to [https://st.suckless.org/](https://st.suckless.org/) for details on the
 
 ### Changelog:
 
+2021-05-09 - Added the sync patch
+
 2021-05-08 - Added blinking cursor, delkey, undercurl,universcroll, desktopentry, netwmicon and osc_10_11_12_2 patches
 
 2021-05-07 - Added xresources reload patch
@@ -184,6 +186,11 @@ Refer to [https://st.suckless.org/](https://st.suckless.org/) for details on the
    - [spoiler](https://st.suckless.org/patches/spoiler/)
       - use inverted defaultbg/fg for selection when bg/fg are the same
 
+   - [sync](https://st.suckless.org/patches/sync/)
+      - adds synchronized-updates/application-sync support in st
+      - this has no effect except when an application uses the synchronized-update escape sequences
+      - with this patch nearly all cursor flicker is eliminated in tmux, and tmux detects it automatically via terminfo
+
    - [themed-cursor](https://st.suckless.org/patches/themed_cursor/)
       - instead of a default X cursor, use the xterm cursor from your cursor theme
 
diff --git a/config.def.h b/config.def.h
index 84a639d..c6d37bd 100644
--- a/config.def.h
+++ b/config.def.h
@@ -74,6 +74,14 @@ int allowwindowops = 0;
 static double minlatency = 8;
 static double maxlatency = 33;
 
+#if SYNC_PATCH
+/*
+ * Synchronized-Update timeout in ms
+ * https://gitlab.com/gnachman/iterm2/-/wikis/synchronized-updates-spec
+ */
+static uint su_timeout = 200;
+#endif // SYNC_PATCH
+
 /*
  * blinking timeout (set to 0 to disable blinking) for the terminal blinking
  * attribute.
diff --git a/patch/st_include.c b/patch/st_include.c
index b33e975..4ef29f9 100644
--- a/patch/st_include.c
+++ b/patch/st_include.c
@@ -25,4 +25,7 @@
 #endif
 #if SIXEL_PATCH
 #include "sixel_st.c"
+#endif
+#if SYNC_PATCH
+#include "sync.c"
 #endif
\ No newline at end of file
diff --git a/patch/st_include.h b/patch/st_include.h
index 3dc496d..93f46c0 100644
--- a/patch/st_include.h
+++ b/patch/st_include.h
@@ -25,4 +25,7 @@
 #endif
 #if SIXEL_PATCH
 #include "sixel_st.h"
+#endif
+#if SYNC_PATCH
+#include "sync.h"
 #endif
\ No newline at end of file
diff --git a/patch/sync.c b/patch/sync.c
new file mode 100644
index 0000000..a0a815c
--- /dev/null
+++ b/patch/sync.c
@@ -0,0 +1,31 @@
+#include <time.h>
+struct timespec sutv;
+
+static void
+tsync_begin()
+{
+	clock_gettime(CLOCK_MONOTONIC, &sutv);
+	su = 1;
+}
+
+static void
+tsync_end()
+{
+	su = 0;
+}
+
+int
+tinsync(uint timeout)
+{
+	struct timespec now;
+	if (su && !clock_gettime(CLOCK_MONOTONIC, &now)
+	       && TIMEDIFF(now, sutv) >= timeout)
+		su = 0;
+	return su;
+}
+
+int
+ttyread_pending()
+{
+	return twrite_aborted;
+}
\ No newline at end of file
diff --git a/patch/sync.h b/patch/sync.h
new file mode 100644
index 0000000..6c2ebe7
--- /dev/null
+++ b/patch/sync.h
@@ -0,0 +1,7 @@
+static int su = 0;
+static int twrite_aborted = 0;
+
+static void tsync_begin();
+static void tsync_end();
+int tinsync(uint timeout);
+int ttyread_pending();
\ No newline at end of file
diff --git a/patches.def.h b/patches.def.h
index 7336e96..e2b2a05 100644
--- a/patches.def.h
+++ b/patches.def.h
@@ -271,6 +271,19 @@
  */
 #define SPOILER_PATCH 0
 
+/* This patch adds synchronized-updates/application-sync support in st.
+ * This will have no effect except when an application uses the synchronized-update escape
+ * sequences. With this patch nearly all cursor flicker is eliminated in tmux, and tmux detects
+ * it automatically via terminfo.
+ *
+ * Note: this patch alters st.info to promote support for extra escape sequences, which can
+ * potentially cause application misbehaviour if you do not use this patch. Try removing or
+ * commenting out the corresponding line in st.info if this is causing issues.
+ *
+ * https://st.suckless.org/patches/sync/
+ */
+#define SYNC_PATCH 0
+
 /* Instead of a default X cursor, use the xterm cursor from your cursor theme.
  * You need to uncomment the corresponding line in config.mk to use the -lXcursor library
  * when including this patch.
@@ -288,6 +301,10 @@
  *                  |  \- sets underline style to curvy
  *                   \- set underline
  *
+ * Note: this patch alters st.info to promote support for extra escape sequences, which can
+ * potentially cause application misbehaviour if you do not use this patch. Try removing or
+ * commenting out the corresponding line in st.info if this is causing issues.
+ *
  * https://st.suckless.org/patches/undercurl/
  */
 #define UNDERCURL_PATCH 0
diff --git a/st.c b/st.c
index 1caa949..0f5599e 100644
--- a/st.c
+++ b/st.c
@@ -904,7 +904,11 @@ ttyread(void)
 	int ret, written;
 
 	/* append read bytes to unprocessed bytes */
+	#if SYNC_PATCH
+	ret = twrite_aborted ? 1 : read(cmdfd, buf+buflen, LEN(buf)-buflen);
+	#else
 	ret = read(cmdfd, buf+buflen, LEN(buf)-buflen);
+	#endif // SYNC_PATCH
 
 	switch (ret) {
 	case 0:
@@ -912,7 +916,11 @@ ttyread(void)
 	case -1:
 		die("couldn't read from shell: %s\n", strerror(errno));
 	default:
+		#if SYNC_PATCH
+		buflen += twrite_aborted ? 0 : ret;
+		#else
 		buflen += ret;
+		#endif // SYNC_PATCH
 		written = twrite(buf, buflen, 0);
 		buflen -= written;
 		/* keep any incomplete UTF-8 byte sequence for the next call */
@@ -1077,6 +1085,9 @@ tsetdirtattr(int attr)
 void
 tfulldirt(void)
 {
+	#if SYNC_PATCH
+	tsync_end();
+	#endif // SYNC_PATCH
 	tsetdirt(0, term.row-1);
 }
 
@@ -2241,8 +2252,17 @@ strhandle(void)
 				tnewline(1);
 			}
 		}
-		return;
 		#endif // SIXEL_PATCH
+		#if SYNC_PATCH
+		/* https://gitlab.com/gnachman/iterm2/-/wikis/synchronized-updates-spec */
+		if (strstr(strescseq.buf, "=1s") == strescseq.buf)
+			tsync_begin();  /* BSU */
+		else if (strstr(strescseq.buf, "=2s") == strescseq.buf)
+			tsync_end();  /* ESU */
+		#endif // SYNC_PATCH
+		#if SIXEL_PATCH || SYNC_PATCH
+		return;
+		#endif // SIXEL_PATCH | SYNC_PATCH
 	case '_': /* APC -- Application Program Command */
 	case '^': /* PM -- Privacy Message */
 		return;
@@ -2834,6 +2854,11 @@ twrite(const char *buf, int buflen, int show_ctrl)
 	Rune u;
 	int n;
 
+	#if SYNC_PATCH
+	int su0 = su;
+	twrite_aborted = 0;
+	#endif // SYNC_PATCH
+
 	for (n = 0; n < buflen; n += charsize) {
 		#if SIXEL_PATCH
 		if (IS_SET(MODE_UTF8) && !IS_SET(MODE_SIXEL))
@@ -2849,6 +2874,12 @@ twrite(const char *buf, int buflen, int show_ctrl)
 			u = buf[n] & 0xFF;
 			charsize = 1;
 		}
+		#if SYNC_PATCH
+		if (su0 && !su) {
+			twrite_aborted = 1;
+			break;  // ESU - allow rendering before a new BSU
+		}
+		#endif // SYNC_PATCH
 		if (show_ctrl && ISCONTROL(u)) {
 			if (u & 0x80) {
 				u &= 0x7f;
diff --git a/st.info b/st.info
index 659878c..a45d8de 100644
--- a/st.info
+++ b/st.info
@@ -1,4 +1,5 @@
 st-mono| simpleterm monocolor,
+# undercurl patch / UNDERCURL_PATCH
 	Su,
 	acsc=+C\,D-A.B0E``aaffgghFiGjjkkllmmnnooppqqrrssttuuvvwwxxyyzz{{||}}~~,
 	am,
@@ -192,6 +193,8 @@ st-mono| simpleterm monocolor,
 	Ms=\E]52;%p1%s;%p2%s\007,
 	Se=\E[2 q,
 	Ss=\E[%p1%d q,
+# sync patch / SYNC_PATCH
+	Sync=\EP=%p1%ds\E\\,
 
 st| simpleterm,
 	use=st-mono,
diff --git a/x.c b/x.c
index c8fffe0..b0b7709 100644
--- a/x.c
+++ b/x.c
@@ -2539,7 +2539,11 @@ run(void)
 		FD_SET(ttyfd, &rfd);
 		FD_SET(xfd, &rfd);
 
+		#if SYNC_PATCH
+		if (XPending(xw.dpy) || ttyread_pending())
+		#else
 		if (XPending(xw.dpy))
+		#endif // SYNC_PATCH
 			timeout = 0;  /* existing events might not set xfd */
 
 		seltv.tv_sec = timeout / 1E3;
@@ -2553,8 +2557,14 @@ run(void)
 		}
 		clock_gettime(CLOCK_MONOTONIC, &now);
 
+		#if SYNC_PATCH
+		int ttyin = FD_ISSET(ttyfd, &rfd) || ttyread_pending();
+		if (ttyin)
+			ttyread();
+		#else
 		if (FD_ISSET(ttyfd, &rfd))
 			ttyread();
+		#endif // SYNC_PATCH
 
 		xev = 0;
 		while (XPending(xw.dpy)) {
@@ -2577,7 +2587,12 @@ run(void)
 		 * maximum latency intervals during `cat huge.txt`, and perfect
 		 * sync with periodic updates from animations/key-repeats/etc.
 		 */
-		if (FD_ISSET(ttyfd, &rfd) || xev) {
+		#if SYNC_PATCH
+		if (ttyin || xev)
+		#else
+		if (FD_ISSET(ttyfd, &rfd) || xev)
+		#endif // SYNC_PATCH
+		{
 			if (!drawing) {
 				trigger = now;
 				#if BLINKING_CURSOR_PATCH
@@ -2594,6 +2609,20 @@ run(void)
 				continue;  /* we have time, try to find idle */
 		}
 
+		#if SYNC_PATCH
+		if (tinsync(su_timeout)) {
+			/*
+			 * on synchronized-update draw-suspension: don't reset
+			 * drawing so that we draw ASAP once we can (just after
+			 * ESU). it won't be too soon because we already can
+			 * draw now but we skip. we set timeout > 0 to draw on
+			 * SU-timeout even without new content.
+			 */
+			timeout = minlatency;
+			continue;
+		}
+		#endif // SYNC_PATCH
+
 		/* idle detected or maxlatency exhausted -> draw */
 		timeout = -1;
 		#if BLINKING_CURSOR_PATCH