diff --git a/flight/PiOS/Common/pios_hmc5843.c b/flight/PiOS/Common/pios_hmc5843.c
index 52506af1f..58eeb98be 100644
--- a/flight/PiOS/Common/pios_hmc5843.c
+++ b/flight/PiOS/Common/pios_hmc5843.c
@@ -102,7 +102,7 @@ typedef struct {
 } PIOS_HMC5843_ConfigTypeDef;
 
 /* Local Variables */
-static bool pios_hmc5843_data_ready;
+volatile bool pios_hmc5843_data_ready;
 
 static void PIOS_HMC5843_Config(PIOS_HMC5843_ConfigTypeDef *HMC5843_Config_Struct);
 static bool PIOS_HMC5843_Read(uint8_t address, uint8_t *buffer, uint8_t len);