diff --git a/tools/sdk/include/mem.h b/tools/sdk/include/mem.h
index 9fe13a8bf..c9231af8e 100644
--- a/tools/sdk/include/mem.h
+++ b/tools/sdk/include/mem.h
@@ -43,7 +43,8 @@ bool ICACHE_FLASH_ATTR check_memleak_debug_enable(void)
 #define os_malloc malloc
 #define os_calloc calloc
 #define os_realloc realloc
-#define os_zalloc zalloc
+#define os_zalloc(s) calloc(1,s)
+#define zalloc(s) calloc(1,s)
 
 #ifndef MEMLEAK_DEBUG
 #define MEMLEAK_DEBUG_ENABLE	0
diff --git a/tools/sdk/lib/liblwip2.a b/tools/sdk/lib/liblwip2.a
index ac55498a1..451dd36c6 100644
Binary files a/tools/sdk/lib/liblwip2.a and b/tools/sdk/lib/liblwip2.a differ
diff --git a/tools/sdk/lib/liblwip2_1460.a b/tools/sdk/lib/liblwip2_1460.a
index 1458c584a..62bb4c02c 100644
Binary files a/tools/sdk/lib/liblwip2_1460.a and b/tools/sdk/lib/liblwip2_1460.a differ
diff --git a/tools/sdk/lwip2/README.md b/tools/sdk/lwip2/README.md
index cb6b2d793..406307101 100644
--- a/tools/sdk/lwip2/README.md
+++ b/tools/sdk/lwip2/README.md
@@ -1,10 +1,13 @@
+```make install```: download, compile, install lwip2
 
-make install	download, compile, install lwip2
-make download	download lwIP-2 builder
-make clean	clean builder only
+```make download```: download lwIP-2 builder
+
+```make clean```: clean builder only
 
 glue and lwIP debug options are in builder/glue/gluedebug.h
+
 MSS values are in builder/Makefile.arduino
+
 MSS values in boards.txt are only informative
 
 current lwip2 submodule repository: https://github.com/d-a-v/esp82xx-nonos-linklayer/tree/arduino-2.4.0
diff --git a/tools/sdk/lwip2/builder b/tools/sdk/lwip2/builder
index afc929779..1b8826735 160000
--- a/tools/sdk/lwip2/builder
+++ b/tools/sdk/lwip2/builder
@@ -1 +1 @@
-Subproject commit afc929779c7fcf23c6253f0cc71b1cf0bc83183f
+Subproject commit 1b8826735cffa57d71ff6ce1fd79ec9d44a5215f
diff --git a/tools/sdk/lwip2/include/gluedebug.h b/tools/sdk/lwip2/include/gluedebug.h
index 71bc30efc..03c9a1781 100644
--- a/tools/sdk/lwip2/include/gluedebug.h
+++ b/tools/sdk/lwip2/include/gluedebug.h
@@ -8,6 +8,7 @@
 // this is needed separately from lwipopts.h
 // because it is shared by both sides of glue
 
+#define UNDEBUG		1	// 0 or 1 (1: uassert removed)
 #define UDEBUG		0	// 0 or 1 (glue debug)
 #define UDUMP		0	// 0 or 1 (glue / dump packet)
 #define UDEBUGINDEX	0	// 0 or 1 (show debug line number)
@@ -81,8 +82,22 @@ int doprint_minus (const char* format, ...) __attribute__ ((format (printf, 1, 2
 #define uprint(x...)		do { (void)0; } while (0)
 #endif
 
+#if UNDEBUG
+#define uassert(assertion...)   do { (void)0; } while (0)
+#else // !defined(UNDEBUG)
+#define uassert(assertion...)	\
+do { if ((assertion) == 0) { \
+		static const char assrt[] ICACHE_RODATA_ATTR STORE_ATTR = #assertion " wrong@"; \
+		os_printf_plus(assrt); \
+		static const char assrt_file[] ICACHE_RODATA_ATTR STORE_ATTR = __FILE__; \
+		os_printf_plus(assrt_file); \
+		static const char assrt_line[] ICACHE_RODATA_ATTR STORE_ATTR = ":%d\n"; \
+		os_printf_plus(assrt_line, __LINE__); \
+		uhalt(); \
+} } while (0)
+#endif // !defined(UNDEBUG)
+
 #define uerror(x...)		do { doprint(x); } while (0)
-#define uassert(assertion...)	do { if ((assertion) == 0) { os_printf_plus("assert fail: " #assertion " @%s:%d\n", __FILE__, __LINE__); uhalt(); } } while (0)
 #define uhalt() 		do { *((int*)0) = 0; /* this triggers gdb */ } while (0)
 #define nl()			do { uprint("\n"); } while (0)