diff --git a/tools/esp8266/app.cpp b/tools/esp8266/app.cpp
index d45baa62..1b05bf3e 100644
--- a/tools/esp8266/app.cpp
+++ b/tools/esp8266/app.cpp
@@ -283,7 +283,7 @@ void app::loop(void) {
                     }
                 }
             }
-            snprintf(val, 10, "%d", millis()/1000);
+            snprintf(val, 10, "%ld", millis()/1000);
             mMqtt.sendMsg("uptime", val);
         }
 
@@ -480,8 +480,6 @@ void app::showSetup(void) {
     DPRINTLN(DBG_VERBOSE, F("app::showSetup"));
     // overrides same method in main.cpp
 
-    uint16_t interval;
-
     String html = FPSTR(setup_html);
     html.replace(F("{SSID}"), mStationSsid);
     // PWD will be left at the default value (for protection)
@@ -497,7 +495,6 @@ void app::showSetup(void) {
     String inv;
     uint64_t invSerial;
     char name[MAX_NAME_LENGTH + 1] = {0};
-    uint8_t invType;
     uint16_t modPwr[4];
     for(uint8_t i = 0; i < MAX_NUM_INVERTERS; i ++) {
         mEep->read(ADDR_INV_ADDR + (i * 8),               &invSerial);
@@ -802,7 +799,7 @@ void app::saveValues(bool webSend = true) {
             // address
             mWeb->arg("inv" + String(i) + "Addr").toCharArray(buf, 20);
             if(strlen(buf) == 0)
-                snprintf(buf, 20, "\0");
+                memset(buf, 0, 20);
             addr.u64 = Serial2u64(buf);
             mEep->write(ADDR_INV_ADDR + (i * 8), addr.u64);
 
diff --git a/tools/esp8266/debug.h b/tools/esp8266/debug.h
index c1bb23cf..3c5d80a0 100644
--- a/tools/esp8266/debug.h
+++ b/tools/esp8266/debug.h
@@ -6,7 +6,6 @@
 #ifndef __DEBUG_H__
 #define __DEBUG_H__
 
-
 //-----------------------------------------------------------------------------
 // available levels
 #define DBG_ERROR       1
@@ -20,40 +19,44 @@
 // globally used level
 #define DEBUG_LEVEL DBG_INFO
 
-
+#ifdef ARDUINO
+  #include "Arduino.h"
+#endif
 
 #ifdef NDEBUG
     #define DBGPRINT(str)
     #define DBGPRINTLN(str)
 #else
-    #ifndef DSERIAL
-    #define DSERIAL Serial
+    #ifdef ARDUINO
+        #ifndef DSERIAL
+        #define DSERIAL Serial
+        #endif
+
+        template <class T>
+        inline void DBGPRINT(T str) { DSERIAL.print(str); }
+        template <class T>
+        inline void DBGPRINTLN(T str) { DBGPRINT(str); DBGPRINT(F("\r\n")); }
+        inline void DHEX(uint8_t b) {
+            if( b<0x10 ) DSERIAL.print('0');
+            DSERIAL.print(b,HEX);
+        }
+        inline void DHEX(uint16_t b) {
+            if( b<0x10 ) DSERIAL.print(F("000"));
+            else if( b<0x100 ) DSERIAL.print(F("00"));
+            else if( b<0x1000 ) DSERIAL.print(F("0"));
+            DSERIAL.print(b,HEX);
+        }
+        inline void DHEX(uint32_t b) {
+            if( b<0x10 ) DSERIAL.print(F("0000000"));
+            else if( b<0x100 ) DSERIAL.print(F("000000"));
+            else if( b<0x1000 ) DSERIAL.print(F("00000"));
+            else if( b<0x10000 ) DSERIAL.print(F("0000"));
+            else if( b<0x100000 ) DSERIAL.print(F("000"));
+            else if( b<0x1000000 ) DSERIAL.print(F("00"));
+            else if( b<0x10000000 ) DSERIAL.print(F("0"));
+            DSERIAL.print(b,HEX);
+        }
     #endif
-
-    template <class T>
-    inline void DBGPRINT(T str) { DSERIAL.print(str); }
-    template <class T>
-    inline void DBGPRINTLN(T str) { DBGPRINT(str); DBGPRINT(F("\r\n")); }
-    inline void DHEX(uint8_t b) {
-        if( b<0x10 ) DSERIAL.print('0');
-        DSERIAL.print(b,HEX);
-    }
-    inline void DHEX(uint16_t b) {
-        if( b<0x10 ) DSERIAL.print(F("000"));
-        else if( b<0x100 ) DSERIAL.print(F("00"));
-        else if( b<0x1000 ) DSERIAL.print(F("0"));
-        DSERIAL.print(b,HEX);
-    }
-    inline void DHEX(uint32_t b) {
-        if( b<0x10 ) DSERIAL.print(F("0000000"));
-        else if( b<0x100 ) DSERIAL.print(F("000000"));
-        else if( b<0x1000 ) DSERIAL.print(F("00000"));
-        else if( b<0x10000 ) DSERIAL.print(F("0000"));
-        else if( b<0x100000 ) DSERIAL.print(F("000"));
-        else if( b<0x1000000 ) DSERIAL.print(F("00"));
-        else if( b<0x10000000 ) DSERIAL.print(F("0"));
-        DSERIAL.print(b,HEX);
-    }
 #endif
 
 
diff --git a/tools/esp8266/defines.h b/tools/esp8266/defines.h
index 8861bab9..f12bcba6 100644
--- a/tools/esp8266/defines.h
+++ b/tools/esp8266/defines.h
@@ -21,7 +21,7 @@
 //-------------------------------------
 #define VERSION_MAJOR       0
 #define VERSION_MINOR       4
-#define VERSION_PATCH       20
+#define VERSION_PATCH       21
 
 
 //-------------------------------------