diff --git a/src/buffer.c b/src/buffer.c
index e9243d4..4da9d63 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1678,9 +1678,10 @@
     buf->b_fname = buf->b_sfname;
 #ifdef UNIX
     if (st.st_dev == (dev_T)-1)
-	buf->b_dev = -1;
+	buf->b_dev_valid = FALSE;
     else
     {
+	buf->b_dev_valid = TRUE;
 	buf->b_dev = st.st_dev;
 	buf->b_ino = st.st_ino;
     }
@@ -2693,9 +2694,10 @@
     buf->b_fname = buf->b_sfname;
 #ifdef UNIX
     if (st.st_dev == (dev_T)-1)
-	buf->b_dev = -1;
+	buf->b_dev_valid = FALSE;
     else
     {
+	buf->b_dev_valid = TRUE;
 	buf->b_dev = st.st_dev;
 	buf->b_ino = st.st_ino;
     }
@@ -2889,7 +2891,7 @@
 	/* If no struct stat given, get it now */
 	if (stp == NULL)
 	{
-	    if (buf->b_dev < 0 || mch_stat((char *)ffname, &st) < 0)
+	    if (!buf->b_dev_valid || mch_stat((char *)ffname, &st) < 0)
 		st.st_dev = (dev_T)-1;
 	    stp = &st;
 	}
@@ -2926,11 +2928,12 @@
 
     if (buf->b_fname != NULL && mch_stat((char *)buf->b_fname, &st) >= 0)
     {
+	buf->b_dev_valid = TRUE;
 	buf->b_dev = st.st_dev;
 	buf->b_ino = st.st_ino;
     }
     else
-	buf->b_dev = -1;
+	buf->b_dev_valid = FALSE;
 }
 
 /*
@@ -2941,7 +2944,7 @@
     buf_T	*buf;
     struct stat *stp;
 {
-    return (buf->b_dev >= 0
+    return (buf->b_dev_valid
 	    && stp->st_dev == buf->b_dev
 	    && stp->st_ino == buf->b_ino);
 }
diff --git a/src/fileio.c b/src/fileio.c
index 3af64c4..ae656a0 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4416,7 +4416,7 @@
 # endif
 	buf_setino(buf);
     }
-    else if (buf->b_dev < 0)
+    else if (!buf->b_dev_valid)
 	/* Set the inode when creating a new file. */
 	buf_setino(buf);
 #endif
diff --git a/src/structs.h b/src/structs.h
index 7deb5ab..25012d6 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1166,7 +1166,8 @@
     char_u	*b_fname;	/* current file name */
 
 #ifdef UNIX
-    dev_t	b_dev;		/* device number (-1 if not set) */
+    int		b_dev_valid;	/* TRUE when b_dev has a valid number */
+    dev_t	b_dev;		/* device number */
     ino_t	b_ino;		/* inode number */
 #endif
 #ifdef FEAT_CW_EDITOR
diff --git a/src/version.c b/src/version.c
index 5a38f1b..d8be1e6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -677,6 +677,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    170,
+/**/
     169,
 /**/
     168,