diff --git a/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_NRF51822/spi_api.c b/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_NRF51822/spi_api.c
index b403aa4aa5..c773fc2391 100644
--- a/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_NRF51822/spi_api.c
+++ b/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_NRF51822/spi_api.c
@@ -170,7 +170,7 @@ static inline void spi_enable(spi_t *obj, int slave) {
 }
 
 void spi_format(spi_t *obj, int bits, int mode, int slave) {
-    uint32_t config_mode;
+    uint32_t config_mode = 0;
     spi_disable(obj,slave);
     
     if (bits != 8) {