diff --git a/cores/esp8266/WString.cpp b/cores/esp8266/WString.cpp
index 5498f8a23f..46aad5d5a0 100644
--- a/cores/esp8266/WString.cpp
+++ b/cores/esp8266/WString.cpp
@@ -46,12 +46,12 @@ String::String(const __FlashStringHelper *pstr) {
 }
 
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
-String::String(String &&rval) {
+String::String(String &&rval) noexcept {
     init();
     move(rval);
 }
 
-String::String(StringSumHelper &&rval) {
+String::String(StringSumHelper &&rval) noexcept {
     init();
     move(rval);
 }
@@ -224,7 +224,7 @@ String & String::copy(const __FlashStringHelper *pstr, unsigned int length) {
 }
 
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
-void String::move(String &rhs) {
+void String::move(String &rhs) noexcept {
     if (buffer()) {
         if (capacity() >= rhs.len()) {
             memmove_P(wbuffer(), rhs.buffer(), rhs.length() + 1);
@@ -267,13 +267,13 @@ String & String::operator =(const String &rhs) {
 }
 
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
-String & String::operator =(String &&rval) {
+String & String::operator =(String &&rval) noexcept {
     if (this != &rval)
         move(rval);
     return *this;
 }
 
-String & String::operator =(StringSumHelper &&rval) {
+String & String::operator =(StringSumHelper &&rval) noexcept {
     if (this != &rval)
         move(rval);
     return *this;
diff --git a/cores/esp8266/WString.h b/cores/esp8266/WString.h
index fb2f0797f0..8e2db3f9b9 100644
--- a/cores/esp8266/WString.h
+++ b/cores/esp8266/WString.h
@@ -57,8 +57,8 @@ class String {
         String(const String &str);
         String(const __FlashStringHelper *str);
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
-        String(String &&rval);
-        String(StringSumHelper &&rval);
+        String(String &&rval) noexcept;
+        String(StringSumHelper &&rval) noexcept;
 #endif
         explicit String(char c);
         explicit String(unsigned char, unsigned char base = 10);
@@ -96,8 +96,8 @@ class String {
         String & operator =(const char *cstr);
         String & operator = (const __FlashStringHelper *str);
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
-        String & operator =(String &&rval);
-        String & operator =(StringSumHelper &&rval);
+        String & operator =(String &&rval) noexcept;
+        String & operator =(StringSumHelper &&rval) noexcept;
 #endif
 
         // concatenate (works w/ built-in types)
@@ -317,7 +317,7 @@ class String {
         String & copy(const char *cstr, unsigned int length);
         String & copy(const __FlashStringHelper *pstr, unsigned int length);
 #ifdef __GXX_EXPERIMENTAL_CXX0X__
-        void move(String &rhs);
+        void move(String &rhs) noexcept;
 #endif
 };