diff --git a/codec/mjpeg/jpeg.go b/codec/mjpeg/jpeg.go
index dea764d6..0f240c5e 100644
--- a/codec/mjpeg/jpeg.go
+++ b/codec/mjpeg/jpeg.go
@@ -262,7 +262,8 @@ func writeHeader(p *putBuffer, _type, width, height, nbqTab, dri int, qtable []b
 	// Write JFIF header.
 	mark(p, codeAPP0)
 	p.put16(16)
-	p.putBuf([]byte("JFIF\000"))
+	const jfifLabel = "JFIF\000"
+	p.putBuf([]byte(jfifLabel))
 	p.put16(0x0201)
 	p.put8(0)
 	p.put16(1)