diff --git a/src/structs.h b/src/structs.h
index 03fb92e..5df8f84 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -691,6 +691,12 @@
     int		cmod_did_esilent;	// incremented when emsg_silent is
 } cmdmod_T;
 
+typedef enum {
+    MF_DIRTY_NO = 0,		// no dirty blocks
+    MF_DIRTY_YES,		// there are dirty blocks
+    MF_DIRTY_YES_NOSYNC,	// there are dirty blocks, do not sync yet
+} mfdirty_T;
+
 #define MF_SEED_LEN	8
 
 struct memfile
@@ -712,7 +718,7 @@
     blocknr_T	mf_neg_count;		// number of negative blocks numbers
     blocknr_T	mf_infile_count;	// number of pages in the file
     unsigned	mf_page_size;		// number of bytes in a page
-    int		mf_dirty;		// TRUE if there are dirty blocks
+    mfdirty_T	mf_dirty;
 #ifdef FEAT_CRYPT
     buf_T	*mf_buffer;		// buffer this memfile is for
     char_u	mf_seed[MF_SEED_LEN];	// seed for encryption