diff --git a/src/lpc176x/i2c.c b/src/lpc176x/i2c.c
index 50081d50..58761aba 100644
--- a/src/lpc176x/i2c.c
+++ b/src/lpc176x/i2c.c
@@ -29,7 +29,8 @@ i2c_init(void)
     gpio_peripheral(0, 1, 3, 0);
 
     // Set 100Khz frequency
-    uint32_t PCLK = SystemCoreClock / 4, pulse = PCLK / (100000 * 2);
+    enable_peripheral_clock(PCLK_I2C1);
+    uint32_t pclk = SystemCoreClock, pulse = pclk / (100000 * 2);
     LPC_I2C1->I2SCLL = pulse;
     LPC_I2C1->I2SCLH = pulse;
 
diff --git a/src/lpc176x/internal.h b/src/lpc176x/internal.h
index 1ea07df4..e5b0f5dc 100644
--- a/src/lpc176x/internal.h
+++ b/src/lpc176x/internal.h
@@ -5,6 +5,8 @@
 #define PCLK_TIMER0 1
 #define PCLK_UART0 3
 #define PCLK_ADC 12
+#define PCLK_I2C1 19
+#define PCLK_SSP0 21
 void enable_peripheral_clock(uint32_t pclk);
 void gpio_peripheral(int bank, int pin, int func, int pullup);
 
diff --git a/src/lpc176x/spi.c b/src/lpc176x/spi.c
index 92e303d0..8373a39f 100644
--- a/src/lpc176x/spi.c
+++ b/src/lpc176x/spi.c
@@ -23,6 +23,9 @@ spi_init(void)
     gpio_peripheral(0, 17, 2, 0);
     gpio_peripheral(0, 18, 2, 0);
 
+    // Setup clock
+    enable_peripheral_clock(PCLK_SSP0);
+
     // Set initial registers
     LPC_SSP0->CR0 = 0x07;
     LPC_SSP0->CPSR = 254;
@@ -40,7 +43,7 @@ spi_setup(uint32_t bus, uint8_t mode, uint32_t rate)
 
     // Setup clock rate and mode
     struct spi_config res = {0, 0};
-    uint32_t pclk = SystemCoreClock / 4;
+    uint32_t pclk = SystemCoreClock;
     uint32_t div = DIV_ROUND_UP(pclk/2, rate) << 1;
     res.cpsr = div < 2 ? 2 : (div > 254 ? 254 : div);
     res.cr0 = 0x07 | (mode << 6);