diff --git a/bacnet-stack/ports/at91sam7s/isr.h b/bacnet-stack/ports/at91sam7s/isr.h
index 79b4511b..b8d89dfb 100644
--- a/bacnet-stack/ports/at91sam7s/isr.h
+++ b/bacnet-stack/ports/at91sam7s/isr.h
@@ -28,6 +28,16 @@
 
 #include <stdint.h>
 
+#if defined(__ICCARM__)
+#include <intrinsics.h>
+#define isr_enable() __enable_interrupt()
+#define isr_disable() __disable_interrupt()
+#endif
+#if defined(__GNUC__)
+#define isr_enable() enableIRQ();enableFIQ();
+#define isr_disable() disableFIQ();disableIRQ();
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
diff --git a/bacnet-stack/ports/at91sam7s/main.c b/bacnet-stack/ports/at91sam7s/main.c
index df2c5e02..69750424 100644
--- a/bacnet-stack/ports/at91sam7s/main.c
+++ b/bacnet-stack/ports/at91sam7s/main.c
@@ -185,8 +185,7 @@ int main(
     init();
     bacnet_init();
     /* enable interrupts */
-    enableIRQ();
-    enableFIQ();
+    isr_enable();
     /* broadcast an I-Am on startup */
     Send_I_Am(&Handler_Transmit_Buffer[0]);
     /* endless blink loop */
diff --git a/bacnet-stack/ports/at91sam7s/timer.c b/bacnet-stack/ports/at91sam7s/timer.c
index 2003c12a..6c7cee2b 100644
--- a/bacnet-stack/ports/at91sam7s/timer.c
+++ b/bacnet-stack/ports/at91sam7s/timer.c
@@ -303,7 +303,7 @@ static void Timer0IrqHandler(
 {
 
     volatile AT91PS_TC pTC = AT91C_BASE_TC0;    /* pointer to timer channel 0 register structure */
-    unsigned int dummy; /* temporary */
+    volatile unsigned int dummy; /* temporary */
 
     /* read TC0 Status Register to clear interrupt */
     dummy = pTC->TC_SR;