diff --git a/flight/PiOS/STM32F10x/Libraries/CMSIS/Core/CM3/core_cm3.c b/flight/PiOS/STM32F10x/Libraries/CMSIS/Core/CM3/core_cm3.c
index 0e8c3c43c..d202e369b 100755
--- a/flight/PiOS/STM32F10x/Libraries/CMSIS/Core/CM3/core_cm3.c
+++ b/flight/PiOS/STM32F10x/Libraries/CMSIS/Core/CM3/core_cm3.c
@@ -767,7 +767,7 @@ uint32_t __STREXW(uint32_t value, uint32_t *addr)
 {
    uint32_t result=0;
   
-   __ASM volatile ("strex %0, %2, [%1]" : "=r" (result) : "r" (addr), "r" (value) );
+   __ASM volatile ("strex %0, %2, [%1]" : "=&r" (result) : "r" (addr), "r" (value) );
    return(result);
 }