diff --git a/cache.h b/cache.h
index cc872440ef8..e6b716495d6 100644
--- a/cache.h
+++ b/cache.h
@@ -428,6 +428,7 @@ extern char *git_commit_encoding;
 extern char *git_log_output_encoding;
 
 extern int copy_fd(int ifd, int ofd);
+extern void read_or_die(int fd, void *buf, size_t count);
 extern void write_or_die(int fd, const void *buf, size_t count);
 extern int write_or_whine(int fd, const void *buf, size_t count, const char *msg);
 
diff --git a/write_or_die.c b/write_or_die.c
index bfe4eeb6494..8cf6486025a 100644
--- a/write_or_die.c
+++ b/write_or_die.c
@@ -1,5 +1,21 @@
 #include "cache.h"
 
+void read_or_die(int fd, void *buf, size_t count)
+{
+	char *p = buf;
+	ssize_t loaded;
+
+	while (count > 0) {
+		loaded = xread(fd, p, count);
+		if (loaded == 0)
+			die("unexpected end of file");
+		else if (loaded < 0)
+			die("read error (%s)", strerror(errno));
+		count -= loaded;
+		p += loaded;
+	}
+}
+
 void write_or_die(int fd, const void *buf, size_t count)
 {
 	const char *p = buf;