diff --git a/cores/arduino/Arduino.h b/cores/arduino/Arduino.h
index 199e65e22..d78acd9b4 100644
--- a/cores/arduino/Arduino.h
+++ b/cores/arduino/Arduino.h
@@ -27,6 +27,9 @@
 #define RAMEND   (RAMSTART + RAMSIZE - 1)
 
 #ifdef __cplusplus
+
+using namespace arduino;
+
 extern "C"{
 #endif // __cplusplus
 
diff --git a/cores/arduino/USB/CDC.cpp b/cores/arduino/USB/CDC.cpp
index e1a133ca8..c8314c2bb 100644
--- a/cores/arduino/USB/CDC.cpp
+++ b/cores/arduino/USB/CDC.cpp
@@ -28,6 +28,8 @@
 
 #ifdef CDC_ENABLED
 
+using namespace arduino;
+
 extern USBDevice_SAMD21G18x usbd;
 
 #define CDC_SERIAL_BUFFER_SIZE	256
diff --git a/cores/arduino/USB/SAMD21_USBDevice.h b/cores/arduino/USB/SAMD21_USBDevice.h
index 3fff6e1b8..98a95ce95 100644
--- a/cores/arduino/USB/SAMD21_USBDevice.h
+++ b/cores/arduino/USB/SAMD21_USBDevice.h
@@ -396,7 +396,7 @@ class DoubleBufferedEPOutHandler : public EPHandler {
 private:
 	USBDevice_SAMD21G18x &usbd;
 
-	RingBuffer _rx_buffer;
+	arduino::RingBuffer _rx_buffer;
 
 	const uint32_t ep;
 	volatile uint32_t current, incoming;
diff --git a/cores/arduino/USB/USBAPI.h b/cores/arduino/USB/USBAPI.h
index c5cec6257..07633825d 100644
--- a/cores/arduino/USB/USBAPI.h
+++ b/cores/arduino/USB/USBAPI.h
@@ -35,10 +35,6 @@
 #include "api/USBAPI.h"
 #include "CDC.h"
 
-#if ARDUINO_API_VERSION > 10000
-using namespace arduino;
-#endif
-
 //================================================================================
 // USB
 
@@ -59,9 +55,9 @@ class USBDeviceClass {
 	void standby();
 
 	// Setup API
-	bool handleClassInterfaceSetup(USBSetup &setup);
-	bool handleStandardSetup(USBSetup &setup);
-	bool sendDescriptor(USBSetup &setup);
+	bool handleClassInterfaceSetup(arduino::USBSetup &setup);
+	bool handleStandardSetup(arduino::USBSetup &setup);
+	bool sendDescriptor(arduino::USBSetup &setup);
 
 	// Control EndPoint API
 	uint32_t sendControl(const void *data, uint32_t len);
@@ -100,7 +96,7 @@ extern USBDeviceClass USBDevice;
 //================================================================================
 //	Serial over CDC (Serial1 is the physical port)
 
-class Serial_ : public Stream, public arduino::PluggableUSBModule
+class Serial_ : public arduino::Stream, public arduino::PluggableUSBModule
 {
 public:
 	Serial_(USBDeviceClass &_usb);
@@ -163,8 +159,8 @@ class Serial_ : public Stream, public arduino::PluggableUSBModule
 protected:
     // Implementation of the PUSBListNode
     int getInterface(uint8_t* interfaceNum);
-    int getDescriptor(USBSetup& setup);
-    bool setup(USBSetup& setup);
+    int getDescriptor(arduino::USBSetup& setup);
+    bool setup(arduino::USBSetup& setup);
     uint8_t getShortName(char* name);
     void handleEndpoint(int ep);
     void enableInterrupt();
diff --git a/cores/arduino/USB/USBCore.cpp b/cores/arduino/USB/USBCore.cpp
index be0bb5612..f8322436f 100644
--- a/cores/arduino/USB/USBCore.cpp
+++ b/cores/arduino/USB/USBCore.cpp
@@ -31,6 +31,7 @@
 #include <stdint.h>
 #include <limits.h>
 
+using namespace arduino;
 
 /*
  * USB Device instance
diff --git a/cores/arduino/Uart.h b/cores/arduino/Uart.h
index d02600b3f..6aa847839 100644
--- a/cores/arduino/Uart.h
+++ b/cores/arduino/Uart.h
@@ -24,7 +24,7 @@
 
 #define SERIAL_BUFFER_SIZE  64
 
-class Uart : public HardwareSerial
+class Uart : public arduino::HardwareSerial
 {
   public:
     Uart(SERCOM *_s, uint8_t _pinRX, uint8_t _pinTX, SercomRXPad _padRX, SercomUartTXPad _padTX);
@@ -46,8 +46,8 @@ class Uart : public HardwareSerial
 
   private:
     SERCOM *sercom;
-    SafeRingBuffer rxBuffer;
-    SafeRingBuffer txBuffer;
+    arduino::SafeRingBuffer rxBuffer;
+    arduino::SafeRingBuffer txBuffer;
 
     uint8_t uc_pinRX;
     uint8_t uc_pinTX;
diff --git a/cores/arduino/main.cpp b/cores/arduino/main.cpp
index 5a59884f6..a6d2cb5f5 100644
--- a/cores/arduino/main.cpp
+++ b/cores/arduino/main.cpp
@@ -51,7 +51,7 @@ int main( void )
   for (;;)
   {
     loop();
-    if (serialEventRun) serialEventRun();
+    if (arduino::serialEventRun) arduino::serialEventRun();
   }
 
   return 0;