diff --git a/cores/esp8266/HardwareSerial.cpp b/cores/esp8266/HardwareSerial.cpp
index 970b16c50..fcca84687 100644
--- a/cores/esp8266/HardwareSerial.cpp
+++ b/cores/esp8266/HardwareSerial.cpp
@@ -608,6 +608,7 @@ size_t HardwareSerial::write(uint8_t c) {
 
     while(_tx_buffer->room() == 0) {
         yield();
+        uart_arm_tx_interrupt(_uart);
     }
 
     _tx_buffer->write(c);
diff --git a/cores/esp8266/cbuf.h b/cores/esp8266/cbuf.h
index 87642510b..ceb6a7b6d 100644
--- a/cores/esp8266/cbuf.h
+++ b/cores/esp8266/cbuf.h
@@ -39,8 +39,12 @@ class cbuf {
         }
 
         size_t room() const {
-            if(_end >= _begin) return _size - (_end - _begin) - 1;
-
+            if(_end >= _begin) {
+                return _size - (_end - _begin) - 1;
+            }
+            if(_begin == _end) {
+                return _size;
+            }
             return _begin - _end - 1;
         }