diff --git a/src/arch/msp430fr5969lp/driver/i2c.cc b/src/arch/msp430fr5969lp/driver/i2c.cc
index f807d00e6c729ddeadff43e8b52c2f9a75e494f1..fe5b37b192458b2727e1b0a56985c81370c3888f 100644
--- a/src/arch/msp430fr5969lp/driver/i2c.cc
+++ b/src/arch/msp430fr5969lp/driver/i2c.cc
@@ -8,16 +8,25 @@
 
 volatile unsigned short old_ifg = 0;
 
+#if (F_CPU / F_I2C) < 45
+inline void await_i2c_int(unsigned int ie_flags, unsigned int ifg_flags) {
+	while (!(UCB0IFG & ifg_flags)) ;
+	if (UCB0IFG & (UCNACKIFG | UCCLTOIFG)) {
+		UCB0IFG &= ~(UCNACKIFG | UCCLTOIFG);
+	}
+}
+#else
 inline void await_i2c_int(unsigned int ie_flags, unsigned int ifg_flags)
 {
 	UCB0IFG = 0;
 	old_ifg = 0;
 	UCB0IE = ie_flags;
-	while (!(old_ifg & ifg_flags)) {
+	do {
 		arch.idle();
-	}
+	} while (!(old_ifg & ifg_flags));
 	UCB0IE = 0;
 }
+#endif
 
 signed char I2C::setup()
 {
diff --git a/src/driver/soft_i2c.cc b/src/driver/soft_i2c.cc
index 6c36b6f14ba04bcbcdaf7afa67c6960929dcaed2..76042f26adfa3ddc05fc87bf392a262db3d77f46 100644
--- a/src/driver/soft_i2c.cc
+++ b/src/driver/soft_i2c.cc
@@ -20,10 +20,10 @@ volatile unsigned char timer_done = 0;
 #define SCL_HIGH gpio.input(scl, 1)
 #define SCL_LOW gpio.output(scl, 0)
 #elif SOFTI2C_PULLUP_EXTERNAL
-#define SDA_HIGH do { gpio.input(sda); gpio.write(sda_pull, 1); } while (0)
-#define SDA_LOW do { gpio.write(sda_pull, 0); gpio.output(sda); } while (0)
-#define SCL_HIGH do { gpio.input(scl); gpio.write(scl_pull, 1); } while (0)
-#define SCL_LOW do { gpio.write(scl_pull, 0); gpio.output(scl); } while (0)
+#define SDA_HIGH { gpio.input(sda); gpio.write(sda_pull, 1); }
+#define SDA_LOW { gpio.write(sda_pull, 0); gpio.output(sda); }
+#define SCL_HIGH { gpio.input(scl); gpio.write(scl_pull, 1); }
+#define SCL_LOW { gpio.write(scl_pull, 0); gpio.output(scl); }
 #else /* !SOFTI2C_PULLUP_{INTERNAL,EXTERNAL} */
 #define SDA_HIGH gpio.input(sda)
 #define SDA_LOW gpio.output(sda)