diff --git a/base.h b/base.h
index 777813f..11cb10a 100644
--- a/base.h
+++ b/base.h
@@ -32,8 +32,10 @@ typedef ssize_t Isz;
 
 typedef char Glyph;
 
+typedef Glyph* Field_buffer;
+
 typedef struct {
-  Glyph* buffer;
+  Field_buffer buffer;
   U16 height;
   U16 width;
 } Field;
diff --git a/mark.h b/mark.h
index d206104..e11172f 100644
--- a/mark.h
+++ b/mark.h
@@ -8,7 +8,7 @@ typedef enum {
   Mark_flag_lock = 1 << 2,
   Mark_flag_output = 1 << 3,
   Mark_flag_sleep_phase0 = 1 << 4,
-  Mark_flag_sleep_phase1 = 1 << 4,
+  Mark_flag_sleep_phase1 = 1 << 5,
 } Mark_flags;
 
 typedef U8* Markmap_buffer;