diff --git a/msys2-runtime/0045-Cygwin-signal-Do-not-handle-signal-when-__SIGFLUSHFA.patch b/msys2-runtime/0045-Cygwin-signal-Do-not-handle-signal-when-__SIGFLUSHFA.patch
new file mode 100644
index 00000000000..56737418f1e
--- /dev/null
+++ b/msys2-runtime/0045-Cygwin-signal-Do-not-handle-signal-when-__SIGFLUSHFA.patch
@@ -0,0 +1,88 @@
+From 33799c250f0a7d353cfc34961c7bba26d3a4219a Mon Sep 17 00:00:00 2001
+From: Takashi Yano <takashi.yano@nifty.ne.jp>
+Date: Mon, 23 Dec 2024 10:33:25 +0900
+Subject: [PATCH 45/N] Cygwin: signal: Do not handle signal when
+ __SIGFLUSHFAST is sent
+
+After the commit d243e51ef1d3, zsh sometimes hangs at startup. This
+occurs because SIGCHLD, which should trigger sigsuspend(), is handled
+in cygwait() that is used to wait for a wakeup event in sig_send(),
+even when __SIGFLUSHFAST is sent. Despite __SIGFLUSHFAST being
+required to return before handling the signal, this does not happen.
+With this patch, if the signal currently being sent is __SIGFLUSHFAST,
+do not handle the received signal and keep it asserted after the
+cygwait() for the wakeup event.  Apply the same logic to the cygwait()
+in the retrying loop for WriteFile() as well.
+
+Applied-from: https://inbox.sourceware.org/cygwin-patches/20241223013332.1269-1-takashi.yano@nifty.ne.jp
+Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256954.html
+Fixes: d243e51ef1d3 ("Cygwin: signal: Fix deadlock between main thread and sig thread")
+Reported-by: Daisuke Fujimura <booleanlabel@gmail.com>
+Reviewed-by:
+Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
+Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
+---
+ winsup/cygwin/release/3.5.6 |  5 +++++
+ winsup/cygwin/sigproc.cc    | 20 +++++++++++++++-----
+ 2 files changed, 20 insertions(+), 5 deletions(-)
+ create mode 100644 winsup/cygwin/release/3.5.6
+
+diff --git a/winsup/cygwin/release/3.5.6 b/winsup/cygwin/release/3.5.6
+new file mode 100644
+index 0000000..643d58e
+--- /dev/null
++++ b/winsup/cygwin/release/3.5.6
+@@ -0,0 +1,5 @@
++Fixes:
++------
++
++- Fix zsh hang at startup.
++  Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256954.html
+diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
+index cf43aa9..c298527 100644
+--- a/winsup/cygwin/sigproc.cc
++++ b/winsup/cygwin/sigproc.cc
+@@ -751,10 +751,14 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
+       res = WriteFile (sendsig, leader, packsize, &nb, NULL);
+       if (!res || packsize == nb)
+ 	break;
+-      if (cygwait (NULL, 10, cw_sig_eintr) == WAIT_SIGNALED)
++      if (cygwait (NULL, 10, cw_sig_eintr) == WAIT_SIGNALED
++	  && pack.si.si_signo != __SIGFLUSHFAST)
+ 	_my_tls.call_signal_handler ();
+       res = 0;
+     }
++  /* Re-assert signal_arrived which has been cleared in cygwait(). */
++  if (_my_tls.sig)
++    _my_tls.set_signal_arrived ();
+ 
+   if (!res)
+     {
+@@ -785,7 +789,16 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
+   if (wait_for_completion)
+     {
+       sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup);
+-      rc = cygwait (pack.wakeup, WSSC);
++      do
++	{
++	  rc = cygwait (pack.wakeup, WSSC, cw_sig_eintr);
++	  if (rc == WAIT_SIGNALED && pack.si.si_signo != __SIGFLUSHFAST)
++	    _my_tls.call_signal_handler ();
++	}
++      while (rc != WAIT_OBJECT_0 && rc != WAIT_TIMEOUT);
++      /* Re-assert signal_arrived which has been cleared in cygwait(). */
++      if (_my_tls.sig)
++	_my_tls.set_signal_arrived ();
+       ForceCloseHandle (pack.wakeup);
+     }
+   else
+@@ -806,9 +819,6 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
+       rc = -1;
+     }
+ 
+-  if (wait_for_completion && si.si_signo != __SIGFLUSHFAST)
+-    _my_tls.call_signal_handler ();
+-
+ out:
+   if (communing && rc)
+     {
diff --git a/msys2-runtime/PKGBUILD b/msys2-runtime/PKGBUILD
index 6a41707ac35..1a78676491c 100644
--- a/msys2-runtime/PKGBUILD
+++ b/msys2-runtime/PKGBUILD
@@ -4,7 +4,7 @@
 pkgbase=msys2-runtime
 pkgname=('msys2-runtime' 'msys2-runtime-devel')
 pkgver=3.5.5
-pkgrel=1
+pkgrel=2
 pkgdesc="Cygwin POSIX emulation engine"
 arch=('x86_64')
 url="https://www.cygwin.com/"
@@ -72,7 +72,8 @@ source=('msys2-runtime'::git://sourceware.org/git/newlib-cygwin.git#tag=cygwin-$
         0041-cygthread-suspend-thread-before-terminating.patch
         0042-Cygwin-revert-use-of-CancelSyncronousIo-on-wait_thre.patch
         0043-Cygwin-cache-IsWow64Process2-host-arch-in-wincap.patch
-        0044-Cygwin-uname-add-host-machine-tag-to-sysname.patch)
+        0044-Cygwin-uname-add-host-machine-tag-to-sysname.patch
+        0045-Cygwin-signal-Do-not-handle-signal-when-__SIGFLUSHFA.patch)
 sha256sums=('0c6fcf91be78369e753deb1963b4a04e0db613194e70a7ec653774b028adf509'
             '76e37d572d2aba473aab8f5a1984af2084e6069f9195795c71bc45778edbd1eb'
             '5c79b09f9337cc8a5f993db6dd1f54df269f8390ab3348a94e5a139a5d060e39'
@@ -117,7 +118,8 @@ sha256sums=('0c6fcf91be78369e753deb1963b4a04e0db613194e70a7ec653774b028adf509'
             'eac80fb3b54dced1e982c01a755c1914eccd1f8d74b7b88a0af43819ab317a2f'
             '29c3412a1c7b0e4e719b64337ba5508b141037884ba96e9bee5f8ea253811aa3'
             '7064362256cb558fe443469b5f9988ca927667b7cf13f1c1020aca98e616f900'
-            'fb6c38381eb4f36338a5184f79c98e6046c9ff741da37f2f38f4757c8714ca92')
+            'fb6c38381eb4f36338a5184f79c98e6046c9ff741da37f2f38f4757c8714ca92'
+            '84bbe9320fe9fdc8bf6af88c9ae68eaff4bc8e162ba58ba7422bbd053e88a986')
 
 # Helper macros to help make tasks easier #
 apply_patch_with_msg() {
@@ -198,7 +200,8 @@ prepare() {
   0041-cygthread-suspend-thread-before-terminating.patch \
   0042-Cygwin-revert-use-of-CancelSyncronousIo-on-wait_thre.patch \
   0043-Cygwin-cache-IsWow64Process2-host-arch-in-wincap.patch \
-  0044-Cygwin-uname-add-host-machine-tag-to-sysname.patch
+  0044-Cygwin-uname-add-host-machine-tag-to-sysname.patch \
+  0045-Cygwin-signal-Do-not-handle-signal-when-__SIGFLUSHFA.patch
 }
 
 build() {