diff --git a/src/hsm.h b/src/hsm.h
index 71225c8..a6e6406 100644
--- a/src/hsm.h
+++ b/src/hsm.h
@@ -28,6 +28,10 @@ extern uint32_t board_millis();
    ({ __typeof__ (a) _a = (a); \
        __typeof__ (b) _b = (b); \
      _a < _b ? _a : _b; })
+#define MAX(a,b) \
+   ({ __typeof__ (a) _a = (a); \
+       __typeof__ (b) _b = (b); \
+     _a > _b ? _a : _b; })
 #endif
 #include <string.h>