diff --git a/warc-tiny b/warc-tiny
index 3ffc767..22b7cd7 100755
--- a/warc-tiny
+++ b/warc-tiny
@@ -142,13 +142,15 @@ def iter_warc(f):
 			# Read WARC header
 			while b'\r\n\r\n' not in buf:
 				try:
-					buf = buf + fp.read(16777216)
+					d = fp.read(16777216)
 				except EOFError:
 					break
-				if not buf:
+				if not d:
 					break
+				buf += d
 			if not buf:
 				break
+			assert b'\r\n\r\n' in buf
 			warcHeaderBuf, buf = buf.split(b'\r\n\r\n', 1)
 			assert warcHeaderBuf.startswith(b'WARC/1.0\r\n') or warcHeaderBuf.startswith(b'WARC/1.1\r\n')
 			assert b'\r\nContent-Length:' in warcHeaderBuf