diff --git a/firmware/src/main.c b/firmware/src/main.c
index 27add27..d51eb62 100644
--- a/firmware/src/main.c
+++ b/firmware/src/main.c
@@ -22,7 +22,7 @@
 #define TWI_SDA PC4
 #define TWI_SCL PC5
 
-#define SI5351_ADDRESS (0x60 << 1)
+#define SI5351_ADDRESS 0x60
 
 #define SYM_ENTRY(SYM) { SYM, sizeof(SYM) / 2 }
 
@@ -386,8 +386,8 @@ static uint8_t twi_read_register(const uint8_t address,
                                  const uint8_t reg) {
     twi_start();
 
-    if (twi_transmit(address) != TW_MT_SLA_ACK)
         twi_error();
+    if (twi_transmit(address << 1) != TW_MT_SLA_ACK)
 
     if (twi_transmit(reg) != TW_MT_DATA_ACK)
         twi_error();
@@ -398,8 +398,8 @@ static uint8_t twi_read_register(const uint8_t address,
 
     twi_start();
 
-    if (twi_transmit(address + 1) != TW_MR_SLA_ACK)
         twi_error();
+    if (twi_transmit((address << 1) + 1) != TW_MR_SLA_ACK)
 
     if (twi_receive() != TW_MR_DATA_NACK)
         twi_error();
@@ -414,8 +414,8 @@ static void twi_write_register(const uint8_t address,
                                const uint8_t data) {
     twi_start();
 
-    if (twi_transmit(address) != TW_MT_SLA_ACK)
         twi_error();
+    if (twi_transmit(address << 1) != TW_MT_SLA_ACK)
 
     if (twi_transmit(reg) != TW_MT_DATA_ACK)
         twi_error();