diff --git a/drivers/Serial.cpp b/drivers/Serial.cpp
index 8e3ce518a53..7f0dcab8229 100644
--- a/drivers/Serial.cpp
+++ b/drivers/Serial.cpp
@@ -15,6 +15,7 @@
  */
 #include "drivers/Serial.h"
 #include "platform/mbed_wait_api.h"
+#include "platform/mbed_critical.h"
 
 #if DEVICE_SERIAL
 
@@ -36,12 +37,42 @@ int Serial::_putc(int c) {
     return _base_putc(c);
 }
 
+int Serial::getc() {
+    // Mutex is already held
+	if(!core_util_is_isr_active())
+	{
+        return Stream::getc();
+	}
+	else
+	{
+        return _base_getc();
+	}
+}
+
+int Serial::putc(int c) {
+    // Mutex is already held
+	if(!core_util_is_isr_active())
+	{
+        return Stream::putc(c);
+	}
+	else
+	{
+        return _base_putc(c);
+	}
+}
+
 void Serial::lock() {
-    _mutex.lock();
+	if(!core_util_is_isr_active())
+	{
+        _mutex.lock();
+	}
 }
 
 void Serial::unlock() {
-    _mutex.unlock();
+	if(!core_util_is_isr_active())
+	{
+        _mutex.unlock();
+	}
 }
 
 } // namespace mbed
diff --git a/drivers/Serial.h b/drivers/Serial.h
index 549943a47c0..296b4b69aea 100644
--- a/drivers/Serial.h
+++ b/drivers/Serial.h
@@ -98,6 +98,8 @@ class Serial : public SerialBase, public Stream, private NonCopyable<Serial> {
     {
         return SerialBase::writeable();
     }
+    int getc();
+    int putc(int c);
 
 protected:
     virtual int _getc();
diff --git a/drivers/SerialBase.cpp b/drivers/SerialBase.cpp
index 5ec47ff83a6..ee0a2279b64 100644
--- a/drivers/SerialBase.cpp
+++ b/drivers/SerialBase.cpp
@@ -55,7 +55,8 @@ void SerialBase::format(int bits, Parity parity, int stop_bits) {
 
 int SerialBase::readable() {
     lock();
-    int ret = serial_readable(&_serial);
+    int ret = 0;
+    ret = serial_readable(&_serial);
     unlock();
     return ret;
 }
@@ -63,7 +64,8 @@ int SerialBase::readable() {
 
 int SerialBase::writeable() {
     lock();
-    int ret = serial_writable(&_serial);
+    int ret = 0;
+    ret = serial_writable(&_serial);
     unlock();
     return ret;
 }