diff --git a/src/simpgmspace.h b/src/simpgmspace.h
index f3374ce34..0597eb9f4 100644
--- a/src/simpgmspace.h
+++ b/src/simpgmspace.h
@@ -291,7 +291,7 @@ extern void rxPdcUsart( void (*pChProcess)(uint8_t x) );
 #define UPE0    0
 #define FE0     0
 
-#define ISR(x...)  void x()
+#define ISR(x, ...)  void x()
 
 #if defined(CPUARM)
 extern volatile uint32_t Tenms;