diff --git a/build/shared/revisions.txt b/build/shared/revisions.txt
index 0582dfd31..441f609de 100644
--- a/build/shared/revisions.txt
+++ b/build/shared/revisions.txt
@@ -3,6 +3,7 @@ ARDUINO 0019
 [core / libraries]
 
 * More accurate delay() function from BenF.
+* Re-enabling PWM after tone() ends.
 
 [environment]
 
diff --git a/hardware/arduino/cores/arduino/wiring_digital.c b/hardware/arduino/cores/arduino/wiring_digital.c
index 1cdbf6c4a..352992360 100755
--- a/hardware/arduino/cores/arduino/wiring_digital.c
+++ b/hardware/arduino/cores/arduino/wiring_digital.c
@@ -36,8 +36,17 @@ void pinMode(uint8_t pin, uint8_t mode)
 	// JWS: can I let the optimizer do this?
 	reg = portModeRegister(port);
 
-	if (mode == INPUT) *reg &= ~bit;
-	else *reg |= bit;
+	if (mode == INPUT) { 
+		uint8_t oldSREG = SREG;
+                cli();
+		*reg &= ~bit;
+		SREG = oldSREG;
+	} else {
+		uint8_t oldSREG = SREG;
+                cli();
+		*reg |= bit;
+		SREG = oldSREG;
+	}
 }
 
 // Forcing this inline keeps the callers from having to push their own stuff
@@ -90,8 +99,17 @@ void digitalWrite(uint8_t pin, uint8_t val)
 
 	out = portOutputRegister(port);
 
-	if (val == LOW) *out &= ~bit;
-	else *out |= bit;
+	if (val == LOW) {
+		uint8_t oldSREG = SREG;
+                cli();
+		*out &= ~bit;
+		SREG = oldSREG;
+	} else {
+		uint8_t oldSREG = SREG;
+                cli();
+		*out |= bit;
+		SREG = oldSREG;
+	}
 }
 
 int digitalRead(uint8_t pin)