diff --git a/cores/esp8266/core_esp8266_postmortem.c b/cores/esp8266/core_esp8266_postmortem.c
index bfb0c06ac3..c93a77fe2e 100644
--- a/cores/esp8266/core_esp8266_postmortem.c
+++ b/cores/esp8266/core_esp8266_postmortem.c
@@ -38,6 +38,7 @@ extern cont_t g_cont;
 static const char* s_panic_file = 0;
 static int s_panic_line = 0;
 static const char* s_panic_func = 0;
+static const char* s_panic_what = 0;
 
 static bool s_abort_called = false;
 
@@ -85,6 +86,11 @@ void __wrap_system_restart_local() {
         ets_puts_P(s_panic_file);
         ets_printf(":%d ", s_panic_line);
         ets_puts_P(s_panic_func);
+        if (s_panic_what) {
+            ets_puts_P(PSTR(": Assertion '"));
+            ets_puts_P(s_panic_what);
+            ets_puts_P(PSTR("' failed."));
+        }
         ets_puts_P(PSTR("\n"));
     }
     else if (s_abort_called) {
@@ -203,10 +209,10 @@ void abort(){
 }
 
 void __assert_func(const char *file, int line, const char *func, const char *what) {
-    (void) what;
     s_panic_file = file;
     s_panic_line = line;
     s_panic_func = func;
+    s_panic_what = what;
     gdb_do_break();
 }
 
diff --git a/libraries/ESP8266WiFi/src/include/ClientContext.h b/libraries/ESP8266WiFi/src/include/ClientContext.h
index b2628f8032..3527d6dee5 100644
--- a/libraries/ESP8266WiFi/src/include/ClientContext.h
+++ b/libraries/ESP8266WiFi/src/include/ClientContext.h
@@ -538,6 +538,7 @@ class ClientContext
     err_t _connected(struct tcp_pcb *pcb, err_t err)
     {
         (void) err;
+        (void) pcb;
         assert(pcb == _pcb);
         assert(_connect_pending);
         esp_schedule();
diff --git a/libraries/ESP8266WiFi/src/include/DataSource.h b/libraries/ESP8266WiFi/src/include/DataSource.h
index 77eb78b676..e5255797cb 100644
--- a/libraries/ESP8266WiFi/src/include/DataSource.h
+++ b/libraries/ESP8266WiFi/src/include/DataSource.h
@@ -31,12 +31,14 @@ class BufferDataSource : public DataSource {
 
     const uint8_t* get_buffer(size_t size) override
     {
+        (void) size;
         assert(_pos + size <= _size);
         return _data + _pos;
     }
 
     void release_buffer(const uint8_t* buffer, size_t size) override
     {
+        (void) buffer;
         assert(buffer == _data + _pos);
         _pos += size;
     }
@@ -69,6 +71,7 @@ class BufferedStreamDataSource : public DataSource {
             _bufferSize = size;
         }
         size_t cb = _stream.readBytes(reinterpret_cast<char*>(_buffer.get()), size);
+        (void) cb;
         assert(cb == size);
         return _buffer.get();
     }
diff --git a/tools/sdk/libc/xtensa-lx106-elf/include/assert.h b/tools/sdk/libc/xtensa-lx106-elf/include/assert.h
index 17b6d85dd7..83801e34e0 100644
--- a/tools/sdk/libc/xtensa-lx106-elf/include/assert.h
+++ b/tools/sdk/libc/xtensa-lx106-elf/include/assert.h
@@ -15,7 +15,7 @@ extern "C" {
 # define assert(__e) ((void)0)
 #else
 # define assert(__e) ((__e) ? (void)0 : __assert_func (PSTR(__FILE__), __LINE__, \
-						       __ASSERT_FUNC, #__e))
+						       __ASSERT_FUNC, PSTR(#__e)))
 
 # ifndef __ASSERT_FUNC
   /* Use g++'s demangled names in C++.  */