diff --git a/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp b/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp
index d9b50a8b7c..7c52ed8486 100644
--- a/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp
+++ b/libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp
@@ -556,7 +556,7 @@ int HTTPClient::sendRequest(const char * type, Stream * stream, size_t size)
     size_t transferred = stream->sendSize(_client.get(), size);
     if (transferred != size)
     {
-        DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] short write, asked for %d but got %d failed.\n", size, transferred);
+        DEBUG_HTTPCLIENT("[HTTP-Client][sendRequest] short write, asked for %zu but got %zu failed.\n", size, transferred);
         esp_yield();
         return returnError(HTTPC_ERROR_SEND_PAYLOAD_FAILED);
     }
diff --git a/libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h b/libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h
index 4c900c9bcd..1be89bbbba 100644
--- a/libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h
+++ b/libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h
@@ -515,7 +515,7 @@ void ESP8266WebServerTemplate<ServerType>::sendContent(Stream* content, ssize_t
   ssize_t sent = content->sendSize(&_currentClient, content_length);
   if (sent != content_length)
   {
-    DBGWS("HTTPServer: error: short send after timeout (%d<%d)\n", sent, content_length);
+    DBGWS("HTTPServer: error: short send after timeout (%zu < %zu)\n", sent, content_length);
   }
   if(_chunked) {
     _currentClient.printf_P(PSTR("\r\n"));
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFi.cpp b/libraries/ESP8266WiFi/src/ESP8266WiFi.cpp
index 8f63a97fa6..6531b3d9df 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFi.cpp
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFi.cpp
@@ -75,12 +75,12 @@ void ESP8266WiFiClass::printDiag(Print& p) {
     char ssid[33]; //ssid can be up to 32chars, => plus null term
     memcpy(ssid, conf.ssid, sizeof(conf.ssid));
     ssid[32] = 0; //nullterm in case of 32 char ssid
-    p.printf_P(PSTR("SSID (%d): %s\n"), strlen(ssid), ssid);
+    p.printf_P(PSTR("SSID (%zu): %s\n"), strlen(ssid), ssid);
 
     char passphrase[65];
     memcpy(passphrase, conf.password, sizeof(conf.password));
     passphrase[64] = 0;
-    p.printf_P(PSTR("Passphrase (%d): %s\n"), strlen(passphrase), passphrase);
+    p.printf_P(PSTR("Passphrase (%zu): %s\n"), strlen(passphrase), passphrase);
 
     p.print(F("BSSID set: "));
     p.println(conf.bssid_set);
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiAP.cpp b/libraries/ESP8266WiFi/src/ESP8266WiFiAP.cpp
index d046a33841..b0a0084853 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFiAP.cpp
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiAP.cpp
@@ -104,13 +104,13 @@ bool ESP8266WiFiAPClass::softAP(const char* ssid, const char* psk, int channel,
 
     size_t ssid_len = ssid ? strlen(ssid) : 0;
     if(ssid_len == 0 || ssid_len > 32) {
-        DEBUG_WIFI("[AP] SSID length %u, too long or missing!\n", ssid_len);
+        DEBUG_WIFI("[AP] SSID length %zu, too long or missing!\n", ssid_len);
         return false;
     }
 
     size_t psk_len = psk ? strlen(psk) : 0;
     if(psk_len > 0 && (psk_len > 64 || psk_len < 8)) {
-        DEBUG_WIFI("[AP] fail psk length %u, too long or short!\n", psk_len);
+        DEBUG_WIFI("[AP] fail psk length %zu, too long or short!\n", psk_len);
         return false;
     }
 
diff --git a/libraries/ESP8266WiFi/src/ESP8266WiFiMulti.cpp b/libraries/ESP8266WiFi/src/ESP8266WiFiMulti.cpp
index 0f6cb72abe..dada704ab1 100644
--- a/libraries/ESP8266WiFi/src/ESP8266WiFiMulti.cpp
+++ b/libraries/ESP8266WiFi/src/ESP8266WiFiMulti.cpp
@@ -328,7 +328,7 @@ wl_status_t ESP8266WiFiMulti::connectWiFiMulti(uint32_t connectTimeoutMs)
 
             // Check SSID
             if (ssid == entry.ssid) {
-                DEBUG_WIFI_MULTI("[WIFIM] Connecting %s\n", ssid);
+                DEBUG_WIFI_MULTI("[WIFIM] Connecting %s\n", ssid.c_str());
 
                 // Connect to WiFi
                 WiFi.begin(ssid, entry.passphrase, channel, bssid);
@@ -361,7 +361,7 @@ wl_status_t ESP8266WiFiMulti::connectWiFiMulti(uint32_t connectTimeoutMs)
         }
     }
 
-    DEBUG_WIFI_MULTI("[WIFIM] Could not connect\n", ssid);
+    DEBUG_WIFI_MULTI("[WIFIM] Could not connect\n");
 
     // Could not connect to any WiFi network
     return WL_CONNECT_FAILED;
diff --git a/libraries/ESP8266mDNS/src/LEAmDNS_Helpers.cpp b/libraries/ESP8266mDNS/src/LEAmDNS_Helpers.cpp
index 60087c16d8..d4014db993 100644
--- a/libraries/ESP8266mDNS/src/LEAmDNS_Helpers.cpp
+++ b/libraries/ESP8266mDNS/src/LEAmDNS_Helpers.cpp
@@ -768,7 +768,7 @@ bool MDNSResponder::_printRRAnswer(const MDNSResponder::stcMDNS_RRAnswer& p_RRAn
         if (pTxts)
         {
             ((/*const c_str()!!*/stcMDNS_RRAnswerTXT*)&p_RRAnswer)->m_Txts.c_str(pTxts);
-            DEBUG_OUTPUT.printf_P(PSTR("TXT(%u) %s"), stTxtLength, pTxts);
+            DEBUG_OUTPUT.printf_P(PSTR("TXT(%zu) %s"), stTxtLength, pTxts);
             delete[] pTxts;
         }
         break;
diff --git a/libraries/ESP8266mDNS/src/LEAmDNS_Structs.cpp b/libraries/ESP8266mDNS/src/LEAmDNS_Structs.cpp
index 85845d8faa..fafe29b98f 100644
--- a/libraries/ESP8266mDNS/src/LEAmDNS_Structs.cpp
+++ b/libraries/ESP8266mDNS/src/LEAmDNS_Structs.cpp
@@ -1666,19 +1666,19 @@ bool MDNSResponder::stcMDNSServiceQuery::stcAnswer::stcTTL::finalTimeoutLevel(vo
 unsigned long MDNSResponder::stcMDNSServiceQuery::stcAnswer::stcTTL::timeout(void) const
 {
 
-    uint32_t    u32Timeout = esp8266::polledTimeout::oneShotMs::neverExpires;
+    unsigned long   timeout = esp8266::polledTimeout::oneShotMs::neverExpires;
 
     if (TIMEOUTLEVEL_BASE == m_timeoutLevel)            // 80%
     {
-        u32Timeout = (m_u32TTL * 800);                  // to milliseconds
+        timeout = (m_u32TTL * 800L);                  // to milliseconds
     }
     else if ((TIMEOUTLEVEL_BASE < m_timeoutLevel) &&    // >80% AND
              (TIMEOUTLEVEL_FINAL >= m_timeoutLevel))    // <= 100%
     {
 
-        u32Timeout = (m_u32TTL * 50);
+        timeout = (m_u32TTL * 50L);
     }   // else: invalid
-    return u32Timeout;
+    return timeout;
 }
 
 
diff --git a/libraries/ESP8266mDNS/src/LEAmDNS_Transfer.cpp b/libraries/ESP8266mDNS/src/LEAmDNS_Transfer.cpp
index 0398d9a6ee..ebe66dff1c 100644
--- a/libraries/ESP8266mDNS/src/LEAmDNS_Transfer.cpp
+++ b/libraries/ESP8266mDNS/src/LEAmDNS_Transfer.cpp
@@ -532,7 +532,7 @@ bool MDNSResponder::_readRRAnswer(MDNSResponder::stcMDNS_RRAnswer*& p_rpRRAnswer
                 if (pTxts)
                 {
                     ((stcMDNS_RRAnswerTXT*&)p_rpRRAnswer)->m_Txts.c_str(pTxts);
-                    DEBUG_OUTPUT.printf_P(PSTR("TXT(%u) %s"), stTxtLength, pTxts);
+                    DEBUG_OUTPUT.printf_P(PSTR("TXT(%zu) %s"), stTxtLength, pTxts);
                     delete[] pTxts;
                 }
                 break;
diff --git a/libraries/LittleFS/examples/SpeedTest/SpeedTest.ino b/libraries/LittleFS/examples/SpeedTest/SpeedTest.ino
index 6fe300f7d9..483494b471 100644
--- a/libraries/LittleFS/examples/SpeedTest/SpeedTest.ino
+++ b/libraries/LittleFS/examples/SpeedTest/SpeedTest.ino
@@ -65,7 +65,7 @@ void DoTest(FS *fs) {
   Serial.printf("==> Time to write %dKB in 256b chunks = %lu milliseconds\n", TESTSIZEKB, stop - start);
 
   f = fs->open("/testwrite.bin", "r");
-  Serial.printf("==> Created file size = %d\n", f.size());
+  Serial.printf("==> Created file size = %zu\n", f.size());
   f.close();
 
   Serial.printf("Reading %dKB file sequentially in 256b chunks\n", TESTSIZEKB);
diff --git a/libraries/LittleFS/src/LittleFS.h b/libraries/LittleFS/src/LittleFS.h
index 65d70aac32..4fea86bddf 100644
--- a/libraries/LittleFS/src/LittleFS.h
+++ b/libraries/LittleFS/src/LittleFS.h
@@ -467,14 +467,14 @@ class LittleFSFileImpl : public FileImpl
                 if (_creation) {
                     int rc = lfs_setattr(_fs->getFS(), _name.get(), 'c', (const void *)&_creation, sizeof(_creation));
                     if (rc < 0) {
-                        DEBUGV("Unable to set creation time on '%s' to %d\n", _name.get(), _creation);
+                        DEBUGV("Unable to set creation time on '%s' to %ld\n", _name.get(), (long)_creation);
                     }
                 }
                 // Add metadata with last write time
                 time_t now = _timeCallback();
                 int rc = lfs_setattr(_fs->getFS(), _name.get(), 't', (const void *)&now, sizeof(now));
                 if (rc < 0) {
-                    DEBUGV("Unable to set last write time on '%s' to %d\n", _name.get(), now);
+                    DEBUGV("Unable to set last write time on '%s' to %ld\n", _name.get(), (long)now);
                 }
             }
         }
diff --git a/libraries/SD/src/SD.h b/libraries/SD/src/SD.h
index eb9372b2a8..b563e2cd09 100644
--- a/libraries/SD/src/SD.h
+++ b/libraries/SD/src/SD.h
@@ -135,8 +135,8 @@ class SDClass {
     size_t size() {
         uint64_t sz = size64();
 #ifdef DEBUG_ESP_PORT
-	if (sz > (uint64_t)SIZE_MAX) {
-            DEBUG_ESP_PORT.printf_P(PSTR("WARNING: SD card size overflow (%lld>= 4GB).  Please update source to use size64().\n"), sz);
+	if (sz > std::numeric_limits<uint32_t>::max()) {
+            DEBUG_ESP_PORT.printf_P(PSTR("WARNING: SD card size overflow (%lld >= 4GB).  Please update source to use size64().\n"), (long long)sz);
         }
 #endif
         return (size_t)sz;
diff --git a/libraries/SDFS/src/SDFS.h b/libraries/SDFS/src/SDFS.h
index 2bc1dc972c..542be537ce 100644
--- a/libraries/SDFS/src/SDFS.h
+++ b/libraries/SDFS/src/SDFS.h
@@ -115,9 +115,9 @@ class SDFSImpl : public FSImpl
         info.maxOpenFiles  = i.maxOpenFiles;
         info.maxPathLength = i.maxPathLength;
 #ifdef DEBUG_ESP_PORT
-        if (i.totalBytes > (uint64_t)SIZE_MAX) {
+        if (i.totalBytes > std::numeric_limits<uint32_t>::max()) {
             // This catches both total and used cases, since used must always be < total.
-            DEBUG_ESP_PORT.printf_P(PSTR("WARNING: SD card size overflow (%lld>= 4GB).  Please update source to use info64().\n"), i.totalBytes);
+            DEBUG_ESP_PORT.printf_P(PSTR("WARNING: SD card size overflow (%lld >= 4GB).  Please update source to use info64().\n"), (long long)i.totalBytes);
         }
 #endif
         info.totalBytes    = (size_t)i.totalBytes;