diff --git a/src/bin/pg_upgrade/file.c b/src/bin/pg_upgrade/file.c
index 5d87408..3d49774 100644
--- a/src/bin/pg_upgrade/file.c
+++ b/src/bin/pg_upgrade/file.c
@@ -22,7 +22,7 @@
 
 
 #ifndef WIN32
-static int	copy_file(const char *fromfile, const char *tofile, bool force);
+static int	copy_file(const char *fromfile, const char *tofile);
 #else
 static int	win32_pghardlink(const char *src, const char *dst);
 #endif
@@ -34,12 +34,12 @@ static int	win32_pghardlink(const char *src, const char *dst);
  *	Copies a relation file from src to dst.
  */
 const char *
-copyFile(const char *src, const char *dst, bool force)
+copyFile(const char *src, const char *dst)
 {
 #ifndef WIN32
-		if (copy_file(src, dst, force) == -1)
+		if (copy_file(src, dst) == -1)
 #else
-		if (CopyFile(src, dst, !force) == 0)
+		if (CopyFile(src, dst, false) == 0)
 #endif
 			return getErrorText();
 		else
@@ -68,7 +68,7 @@ linkFile(const char *src, const char *dst)
 
 #ifndef WIN32
 static int
-copy_file(const char *srcfile, const char *dstfile, bool force)
+copy_file(const char *srcfile, const char *dstfile)
 {
 #define COPY_BUF_SIZE (50 * BLCKSZ)
 
@@ -87,7 +87,7 @@ copy_file(const char *srcfile, const char *dstfile, bool force)
 	if ((src_fd = open(srcfile, O_RDONLY, 0)) < 0)
 		return -1;
 
-	if ((dest_fd = open(dstfile, O_RDWR | O_CREAT | (force ? 0 : O_EXCL), S_IRUSR | S_IWUSR)) < 0)
+	if ((dest_fd = open(dstfile, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR)) < 0)
 	{
 		save_errno = errno;
 
@@ -159,12 +159,13 @@ copy_file(const char *srcfile, const char *dstfile, bool force)
  * VACUUM.
  */
 const char *
-rewriteVisibilityMap(const char *fromfile, const char *tofile, bool force)
+rewriteVisibilityMap(const char *fromfile, const char *tofile)
 {
 	int			src_fd = 0;
 	int			dst_fd = 0;
 	char		buffer[BLCKSZ];
 	ssize_t		bytesRead;
+	ssize_t		totalBytesRead;
 	ssize_t		src_filesize;
 	int			rewriteVmBytesPerPage;
 	BlockNumber new_blkno = 0;
@@ -185,7 +186,7 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile, bool force)
 		return getErrorText();
 	}
 
-	if ((dst_fd = open(tofile, O_RDWR | O_CREAT | (force ? 0 : O_EXCL), S_IRUSR | S_IWUSR)) < 0)
+	if ((dst_fd = open(tofile, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR)) < 0)
 	{
 		close(src_fd);
 		return getErrorText();
@@ -200,13 +201,23 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile, bool force)
 	 * page is empty, we skip it, mostly to avoid turning one-page visibility
 	 * maps for small relations into two pages needlessly.
 	 */
-	while ((bytesRead = read(src_fd, buffer, BLCKSZ)) == BLCKSZ)
+	while (totalBytesRead < src_filesize)
 	{
 		char	   *old_cur;
 		char	   *old_break;
 		char	   *old_blkend;
 		PageHeaderData pageheader;
-		bool		old_lastblk = ((BLCKSZ * (new_blkno + 1)) == src_filesize);
+		bool		old_lastblk;
+
+		if ((bytesRead = read(src_fd, buffer, BLCKSZ)) != BLCKSZ)
+		{
+			close(dst_fd);
+			close(src_fd);
+			return getErrorText();
+		}
+
+		totalBytesRead += BLCKSZ;
+		old_lastblk = (totalBytesRead == src_filesize);
 
 		/* Save the page header data */
 		memcpy(&pageheader, buffer, SizeOfPageHeaderData);
@@ -229,6 +240,9 @@ rewriteVisibilityMap(const char *fromfile, const char *tofile, bool force)
 			bool		empty = true;
 			bool		old_lastpart;
 
+			/* Zero out new_vmbuf */
+			memset(new_vmbuf, 0, sizeof(new_vmbuf));
+
 			/* Copy page header in advance */
 			memcpy(new_vmbuf, &pageheader, SizeOfPageHeaderData);
 
diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h
index 5b00142..10182de 100644
--- a/src/bin/pg_upgrade/pg_upgrade.h
+++ b/src/bin/pg_upgrade/pg_upgrade.h
@@ -367,10 +367,9 @@ bool		pid_lock_file_exists(const char *datadir);
 
 /* file.c */
 
-const char *copyFile(const char *src, const char *dst, bool force);
+const char *copyFile(const char *src, const char *dst);
 const char *linkFile(const char *src, const char *dst);
-const char *rewriteVisibilityMap(const char *fromfile, const char *tofile,
-								 bool force);
+const char *rewriteVisibilityMap(const char *fromfile, const char *tofile);
 
 void		check_hard_link(void);
 FILE	   *fopen_priv(const char *path, const char *mode);
diff --git a/src/bin/pg_upgrade/relfilenode.c b/src/bin/pg_upgrade/relfilenode.c
index 0c1a822..85cb717 100644
--- a/src/bin/pg_upgrade/relfilenode.c
+++ b/src/bin/pg_upgrade/relfilenode.c
@@ -248,9 +248,9 @@ transfer_relfile(FileNameMap *map, const char *type_suffix, bool vm_must_add_fro
 
 			/* Rewrite visibility map if needed */
 			if (vm_must_add_frozenbit && (strcmp(type_suffix, "_vm") == 0))
-				msg = rewriteVisibilityMap(old_file, new_file, true);
+				msg = rewriteVisibilityMap(old_file, new_file);
 			else
-				msg = copyFile(old_file, new_file, true);
+				msg = copyFile(old_file, new_file);
 
 			if (msg)
 				pg_fatal("error while copying relation \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
@@ -262,7 +262,7 @@ transfer_relfile(FileNameMap *map, const char *type_suffix, bool vm_must_add_fro
 
 			/* Rewrite visibility map if needed */
 			if (vm_must_add_frozenbit && (strcmp(type_suffix, "_vm") == 0))
-				msg = rewriteVisibilityMap(old_file, new_file, true);
+				msg = rewriteVisibilityMap(old_file, new_file);
 			else
 				msg = linkFile(old_file, new_file);