diff --git a/.travis.yml b/.travis.yml
index 498739f1cc..36bab4ecf1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,6 +6,14 @@ git:
   depth: 1
   submodules: false
 
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-7
+      - gcc-7
+
 before_install:
   - git submodule update --init  # no recursive update
 
@@ -80,6 +88,7 @@ jobs:
       stage: build
       script: $TRAVIS_BUILD_DIR/tests/ci/host_test.sh
       install: sudo apt-get install valgrind lcov
+      env: CC=gcc-7 CXX=g++-7
 
     - name: "Docs"
       stage: build
@@ -96,6 +105,7 @@ jobs:
     - name: "Mock trivial test"
       stage: build
       script: $TRAVIS_BUILD_DIR/tests/buildm.sh
+      env: CC=gcc-7 CXX=g++-7
 
     - name: "Boards"
       stage: build
diff --git a/cores/esp8266/libb64/cdecode.cpp b/cores/esp8266/libb64/cdecode.cpp
index fcd6f0401a..47c5919dea 100755
--- a/cores/esp8266/libb64/cdecode.cpp
+++ b/cores/esp8266/libb64/cdecode.cpp
@@ -43,6 +43,7 @@ static int base64_decode_block_signed(const int8_t* code_in, const int length_in
           fragment = (int8_t)base64_decode_value_signed(*codechar++);
         } while (fragment < 0);
         *plainchar    = (fragment & 0x03f) << 2;
+        // falls through
       case step_b:
         do {
           if (codechar == code_in+length_in){
@@ -54,6 +55,7 @@ static int base64_decode_block_signed(const int8_t* code_in, const int length_in
         } while (fragment < 0);
         *plainchar++ |= (fragment & 0x030) >> 4;
         *plainchar    = (fragment & 0x00f) << 4;
+        // falls through
       case step_c:
         do {
           if (codechar == code_in+length_in){
@@ -65,6 +67,7 @@ static int base64_decode_block_signed(const int8_t* code_in, const int length_in
         } while (fragment < 0);
         *plainchar++ |= (fragment & 0x03c) >> 2;
         *plainchar    = (fragment & 0x003) << 6;
+        // falls through
       case step_d:
         do {
           if (codechar == code_in+length_in){
diff --git a/cores/esp8266/libb64/cencode.cpp b/cores/esp8266/libb64/cencode.cpp
index 69272faeca..ae8f90a831 100755
--- a/cores/esp8266/libb64/cencode.cpp
+++ b/cores/esp8266/libb64/cencode.cpp
@@ -50,6 +50,7 @@ int base64_encode_block(const char* plaintext_in, int length_in, char* code_out,
       result = (fragment & 0x0fc) >> 2;
       *codechar++ = base64_encode_value(result);
       result = (fragment & 0x003) << 4;
+      // falls through
   case step_B:
       if (plainchar == plaintextend){
         state_in->result = result;
@@ -60,6 +61,7 @@ int base64_encode_block(const char* plaintext_in, int length_in, char* code_out,
       result |= (fragment & 0x0f0) >> 4;
       *codechar++ = base64_encode_value(result);
       result = (fragment & 0x00f) << 2;
+      // falls through
   case step_C:
       if (plainchar == plaintextend){
         state_in->result = result;
diff --git a/libraries/ESP8266AVRISP/src/ESP8266AVRISP.cpp b/libraries/ESP8266AVRISP/src/ESP8266AVRISP.cpp
index 187c917530..0c8aa8451d 100644
--- a/libraries/ESP8266AVRISP/src/ESP8266AVRISP.cpp
+++ b/libraries/ESP8266AVRISP/src/ESP8266AVRISP.cpp
@@ -107,10 +107,9 @@ AVRISPState_t ESP8266AVRISP::serve() {
         case AVRISP_STATE_IDLE:
             // should not be called when idle, error?
             break;
-        case AVRISP_STATE_PENDING: {
+        case AVRISP_STATE_PENDING:
             _state = AVRISP_STATE_ACTIVE;
-        // fallthrough
-        }
+            // falls through
         case AVRISP_STATE_ACTIVE: {
             while (_client.available()) {
                 avrisp();
diff --git a/libraries/ESP8266SdFat b/libraries/ESP8266SdFat
index 2499d4e0c6..6326c71ff1 160000
--- a/libraries/ESP8266SdFat
+++ b/libraries/ESP8266SdFat
@@ -1 +1 @@
-Subproject commit 2499d4e0c60db1a67a47532fc44c17d2d5116e4c
+Subproject commit 6326c71ff1f6294756b6e348edaf723bfe7be3e7
diff --git a/tests/host/Makefile b/tests/host/Makefile
index fd506d3574..6bd73ea61e 100644
--- a/tests/host/Makefile
+++ b/tests/host/Makefile
@@ -153,6 +153,7 @@ FLAGS += -DLWIP_IPV6=0
 FLAGS += -DHOST_MOCK=1
 FLAGS += -DNONOSDK221=1
 FLAGS += $(MKFLAGS)
+FLAGS += -Wimplicit-fallthrough=2 # allow "// fall through" comments to stop spurious warnings
 CXXFLAGS += -std=c++11 -fno-rtti $(FLAGS) -funsigned-char
 CFLAGS += -std=c99 $(FLAGS) -funsigned-char
 LDFLAGS += -coverage $(OPTZ) -g $(M32)
diff --git a/tests/host/common/UdpContextSocket.cpp b/tests/host/common/UdpContextSocket.cpp
index 13c9b2d31c..347c760d80 100644
--- a/tests/host/common/UdpContextSocket.cpp
+++ b/tests/host/common/UdpContextSocket.cpp
@@ -155,6 +155,7 @@ size_t mockUDPFillInBuf (int sock, char* ccinbuf, size_t& ccinbufsize, uint8_t&
 size_t mockUDPPeekBytes (int sock, char* dst, size_t usersize, int timeout_ms, char* ccinbuf, size_t& ccinbufsize)
 {
 	(void) sock;
+	(void) timeout_ms;  
 	if (usersize > CCBUFSIZE)
 		fprintf(stderr, MOCK "CCBUFSIZE(%d) should be increased by %zd bytes (-> %zd)\n", CCBUFSIZE, usersize - CCBUFSIZE, usersize);
 
diff --git a/tests/host/common/include/ClientContext.h b/tests/host/common/include/ClientContext.h
index f9e4a9e3d5..31366ac0dd 100644
--- a/tests/host/common/include/ClientContext.h
+++ b/tests/host/common/include/ClientContext.h
@@ -258,6 +258,9 @@ class ClientContext
 
     void keepAlive (uint16_t idle_sec = TCP_DEFAULT_KEEPALIVE_IDLE_SEC, uint16_t intv_sec = TCP_DEFAULT_KEEPALIVE_INTERVAL_SEC, uint8_t count = TCP_DEFAULT_KEEPALIVE_COUNT)
     {
+        (void) idle_sec;
+        (void) intv_sec;
+        (void) count;
         mockverbose("TODO ClientContext::keepAlive()\n");
     }