diff --git a/lrzip.c b/lrzip.c
index 8fcdc0a..a6ad4a0 100644
--- a/lrzip.c
+++ b/lrzip.c
@@ -57,7 +57,10 @@ void write_magic(rzip_control *control, int fd_in, int fd_out)
 	if (unlikely(fstat(fd_in, &st)))
 		fatal("bad magic file descriptor!?\n");
 
-	memcpy(&magic[6], &control->st_size, 8);
+	/* File size is stored as zero for streaming STDOUT blocks when the
+	 * file size is unknown. */
+	if (!STDIN || !STDOUT || control->eof)
+		memcpy(&magic[6], &control->st_size, 8);
 
 	/* save LZMA compression flags */
 	if (LZMA_COMPRESS) {
diff --git a/lrzip_private.h b/lrzip_private.h
index 9935ee6..bff5b2f 100644
--- a/lrzip_private.h
+++ b/lrzip_private.h
@@ -180,6 +180,7 @@ struct rzip_control {
 	int encrypt;
 	i64 secs;
 	i64 usecs;
+	int eof;
 	md5_ctx ctx;
 	i64 md5_read; // How far into the file the md5 has done so far
 };
diff --git a/rzip.c b/rzip.c
index febe7c7..15bc752 100644
--- a/rzip.c
+++ b/rzip.c
@@ -694,7 +694,7 @@ static void mmap_stdin(rzip_control *control, uchar *buf, struct rzip_state *st)
 			if (unlikely(buf == MAP_FAILED))
 				fatal("Failed to remap to smaller buf in mmap_stdin\n");
 			st->mmap_size = st->chunk_size = total;
-			st->stdin_eof = 1;
+			control->eof = st->stdin_eof = 1;
 			break;
 		}
 		offset_buf += ret;