diff --git a/app/src/parser/micheline_state.h b/app/src/parser/micheline_state.h
index 6584396d7..1f2268e4e 100644
--- a/app/src/parser/micheline_state.h
+++ b/app/src/parser/micheline_state.h
@@ -129,5 +129,5 @@ typedef struct {
         stack[TZ_MICHELINE_STACK_DEPTH];  /// stack of frames
     tz_micheline_parser_frame *frame;     /// current frame
                                           /// init == stack, NULL when done
-    bool is_unit;  /// indicates whether the micheline read is a unit
+    uint8_t is_unit : 1;  /// indicates whether the micheline read is a unit
 } tz_micheline_state;