diff --git a/ext/lwip-1.4.1.zip b/ext/lwip-1.4.1.zip
deleted file mode 100644
index 9b6025ecc..000000000
Binary files a/ext/lwip-1.4.1.zip and /dev/null differ
diff --git a/ext/lwip-1.4.1_patched.zip b/ext/lwip-1.4.1_patched.zip
new file mode 100644
index 000000000..d236a40af
Binary files /dev/null and b/ext/lwip-1.4.1_patched.zip differ
diff --git a/os/various/lwip_bindings/arch/sys_arch.c b/os/various/lwip_bindings/arch/sys_arch.c
index 414a8e7a0..57ed14124 100644
--- a/os/various/lwip_bindings/arch/sys_arch.c
+++ b/os/various/lwip_bindings/arch/sys_arch.c
@@ -90,6 +90,14 @@ void sys_sem_signal(sys_sem_t *sem) {
   chSemSignal(*sem);
 }
 
+/* CHIBIOS FIX: specific variant of this call to be called from within
+   a lock.*/
+void sys_sem_signal_S(sys_sem_t *sem) {
+
+  chSemSignalI(*sem);
+  chSchRescheduleS();
+}
+
 u32_t sys_arch_sem_wait(sys_sem_t *sem, u32_t timeout) {
   systime_t time, tmo;