diff --git a/cores/esp8266/StackThunk.cpp b/cores/esp8266/StackThunk.cpp
index 0d2a8a3541..baa793bdc5 100644
--- a/cores/esp8266/StackThunk.cpp
+++ b/cores/esp8266/StackThunk.cpp
@@ -27,18 +27,26 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>
-#include "pgmspace.h"
+
 #include "debug.h"
 #include "StackThunk.h"
+
+#include <pgmspace.h>
 #include <ets_sys.h>
+
 #include <umm_malloc/umm_malloc.h>
 #include <umm_malloc/umm_heap_select.h>
 
 extern "C" {
 
+extern void optimistic_yield(uint32_t);
+
 uint32_t *stack_thunk_ptr = NULL;
 uint32_t *stack_thunk_top = NULL;
+
 uint32_t *stack_thunk_save = NULL;  /* Saved A1 while in BearSSL */
+uint32_t *stack_thunk_yield_save = NULL;  /* Saved A1 when yielding from within BearSSL */
+
 uint32_t stack_thunk_refcnt = 0;
 
 /* Largest stack usage seen in the wild at  6120 */
@@ -150,4 +158,37 @@ void stack_thunk_fatal_smashing()
     __stack_chk_fail();
 }
 
+/* Called within bearssl code instead of optimistic_yield(...) */
+void stack_thunk_yield();
+asm(
+    ".section     .text.stack_thunk_yield,\"ax\",@progbits\n\t"
+    ".literal_position\n\t"
+    ".align       4\n\t"
+    ".global      stack_thunk_yield\n\t"
+    ".type        stack_thunk_yield, @function\n\t"
+    "\n"
+"stack_thunk_yield:\n\t"
+/* Keep the original caller */
+    "addi         a1, a1, -16\n\t"
+    "s32i.n       a0, a1, 12\n\t"
+/* Swap bearssl <-> cont stacks */
+    "movi         a2, stack_thunk_yield_save\n\t"
+    "s32i.n       a1, a2, 0\n\t"
+    "movi         a2, stack_thunk_save\n\t"
+    "l32i.n       a1, a2, 0\n\t"
+/* optimistic_yield(10000) without extra l32r */
+    "movi         a2, 0x10\n\t"
+    "addmi        a2, a2, 0x2700\n\t"
+    "call0        optimistic_yield\n\t"
+/* Swap bearssl <-> cont stacks, again */
+    "movi         a2, stack_thunk_yield_save\n\t"
+    "l32i.n       a1, a2, 0\n\t"
+    "\n"
+/* Restore caller */
+    "l32i.n       a0, a1, 12\n\t"
+    "addi         a1, a1, 16\n\t"
+    "ret.n\n\t"
+    ".size stack_thunk_yield, .-stack_thunk_yield\n\t"
+);
+
 }
diff --git a/cores/esp8266/StackThunk.h b/cores/esp8266/StackThunk.h
index e72e0efb9f..350775ec24 100644
--- a/cores/esp8266/StackThunk.h
+++ b/cores/esp8266/StackThunk.h
@@ -31,6 +31,8 @@
 extern "C" {
 #endif
 
+extern void stack_thunk_yield(void);
+
 extern void stack_thunk_add_ref();
 extern void stack_thunk_del_ref();
 extern void stack_thunk_repaint();
diff --git a/tools/sdk/include/bearssl/bearssl_git.h b/tools/sdk/include/bearssl/bearssl_git.h
index abdd61ac02..37fe2a0d36 100644
--- a/tools/sdk/include/bearssl/bearssl_git.h
+++ b/tools/sdk/include/bearssl/bearssl_git.h
@@ -1,2 +1,2 @@
 // Do not edit -- Automatically generated by tools/sdk/ssl/bearssl/Makefile
-#define BEARSSL_GIT b024386
+#define BEARSSL_GIT 5166f2b
diff --git a/tools/sdk/lib/libbearssl.a b/tools/sdk/lib/libbearssl.a
index 70352ab2fc..6b9a77e3f6 100644
Binary files a/tools/sdk/lib/libbearssl.a and b/tools/sdk/lib/libbearssl.a differ
diff --git a/tools/sdk/ssl/bearssl b/tools/sdk/ssl/bearssl
index b024386d46..5166f2bb03 160000
--- a/tools/sdk/ssl/bearssl
+++ b/tools/sdk/ssl/bearssl
@@ -1 +1 @@
-Subproject commit b024386d461abd1b7b9be3117e2516b7541f1201
+Subproject commit 5166f2bb03fb03597b0f2c8c7fbcf01616df67c9