diff --git a/cpu/sam0_common/periph/i2c.c b/cpu/sam0_common/periph/i2c.c
index 383f1c55fe..32f27207a5 100644
--- a/cpu/sam0_common/periph/i2c.c
+++ b/cpu/sam0_common/periph/i2c.c
@@ -80,6 +80,9 @@ void i2c_init(i2c_t dev)
 
     assert(dev < I2C_NUMOF);
 
+    const uint32_t fSCL = i2c_config[dev].speed;
+    const uint32_t fGCLK = sam0_gclk_freq(i2c_config[dev].gclk_src);
+
     /* Initialize mutex */
     mutex_init(&locks[dev]);
     /* DISABLE I2C MASTER */
@@ -123,9 +126,9 @@ void i2c_init(i2c_t dev)
     bus(dev)->CTRLB.reg = SERCOM_I2CM_CTRLB_SMEN;
 
     /* Set SPEED */
-    if (i2c_config[dev].speed > I2C_SPEED_FAST_PLUS) {
+    if (fSCL > I2C_SPEED_FAST_PLUS) {
         bus(dev)->CTRLA.reg |= SERCOM_I2CM_CTRLA_SPEED(2);
-    } else if (i2c_config[dev].speed > I2C_SPEED_FAST) {
+    } else if (fSCL > I2C_SPEED_FAST) {
         bus(dev)->CTRLA.reg |= SERCOM_I2CM_CTRLA_SPEED(1);
     } else {
         bus(dev)->CTRLA.reg |= SERCOM_I2CM_CTRLA_SPEED(0);
@@ -134,15 +137,14 @@ void i2c_init(i2c_t dev)
     /* Get the baudrate */
     /* fSCL = fGCLK / (10 + 2 * BAUD)  -> BAUD   = fGCLK / (2 * fSCL) - 5 */
     /* fSCL = fGCLK / (2 + 2 * HSBAUD) -> HSBAUD = fGCLK / (2 * fSCL) - 1 */
-    tmp_baud = (((sam0_gclk_freq(i2c_config[dev].gclk_src) +
-               (2 * (i2c_config[dev].speed)) - 1) / /* round up */
-               (2 * (i2c_config[dev].speed))) -
-               (i2c_config[dev].speed > I2C_SPEED_FAST_PLUS ? 1 : 5));
+    tmp_baud = (fGCLK + (2 * fSCL) - 1) /* round up */
+             / (2 * fSCL)
+             - (fSCL > I2C_SPEED_FAST_PLUS ? 1 : 5);
 
     /* Ensure baudrate is within limits */
     assert(tmp_baud < 255 && tmp_baud > 0);
 
-    if (i2c_config[dev].speed > I2C_SPEED_FAST_PLUS) {
+    if (fSCL > I2C_SPEED_FAST_PLUS) {
         bus(dev)->BAUD.reg = SERCOM_I2CM_BAUD_HSBAUD(tmp_baud);
     } else {
         bus(dev)->BAUD.reg = SERCOM_I2CM_BAUD_BAUD(tmp_baud);