diff --git a/cmd/ractool/data.go b/cmd/ractool/data.go
index 2b4fd4e..543f0ba 100644
--- a/cmd/ractool/data.go
+++ b/cmd/ractool/data.go
@@ -22,10 +22,10 @@
 file, starting at a given offset into the decompressed file, without always
 having to first decompress all of the preceding data.
 
-In comparison to some other popular compression formats, all three of the Zlib,
-Brotli and Zstandard specifications (RFCs 1950, 7932 and 8478) explicitly
-contain the identical phrase: "the data format defined by this specification
-does not attempt to allow random access to compressed data".
+In comparison to some other popular compression formats, all four of the Zlib,
+Brotli, LZ4 and Zstandard specifications explicitly contain the identical
+phrase: "the data format defined by this specification does not attempt to
+allow random access to compressed data".
 
 See the RAC specification for more details:
 https://github.com/google/wuffs/blob/master/doc/spec/rac-spec.md
diff --git a/cmd/ractool/main.go b/cmd/ractool/main.go
index 3ac3df2..27c53bd 100644
--- a/cmd/ractool/main.go
+++ b/cmd/ractool/main.go
@@ -23,10 +23,10 @@
 file, starting at a given offset into the decompressed file, without always
 having to first decompress all of the preceding data.
 
-In comparison to some other popular compression formats, all three of the Zlib,
-Brotli and Zstandard specifications (RFCs 1950, 7932 and 8478) explicitly
-contain the identical phrase: "the data format defined by this specification
-does not attempt to allow random access to compressed data".
+In comparison to some other popular compression formats, all four of the Zlib,
+Brotli, LZ4 and Zstandard specifications explicitly contain the identical
+phrase: "the data format defined by this specification does not attempt to
+allow random access to compressed data".
 
 See the RAC specification for more details:
 https://github.com/google/wuffs/blob/master/doc/spec/rac-spec.md
diff --git a/doc/spec/rac-spec.md b/doc/spec/rac-spec.md
index a14fef2..de6e1e3 100644
--- a/doc/spec/rac-spec.md
+++ b/doc/spec/rac-spec.md
@@ -7,9 +7,10 @@
 
 RAC is a *compressed* file format that allows *random access* (not just
 sequential access) to the decompressed contents. In comparison to some other
-popular compression formats, all three of the
+popular compression formats, all four of the
 [Zlib](https://tools.ietf.org/html/rfc1950),
-[Brotli](https://tools.ietf.org/html/rfc7932) and
+[Brotli](https://tools.ietf.org/html/rfc7932),
+[LZ4](https://github.com/lz4/lz4/blob/master/doc/lz4_Frame_format.md) and
 [Zstandard](https://tools.ietf.org/html/rfc8478) specifications explicitly
 contain the identical phrase: "the data format defined by this specification
 does not attempt to allow random access to compressed data".
@@ -25,7 +26,8 @@
 contains a hierarchical index of those chunks.
 
 RAC is a container format, and while it supports common compression codecs like
-Zlib, Brotli and Zstandard, it is not tied to any particular compression codec.
+Zlib, Brotli, LZ4 and Zstandard, it is not tied to any particular compression
+codec.
 
 Non-goals for version 1 include:
 
@@ -300,7 +302,7 @@
 
   - `0x00` means "RAC + Zeroes".
   - `0x01` means "RAC + Zlib".
-  - `0x02` means "RAC + Brotli".
+  - `0x02` means "RAC + LZ4".
   - `0x04` means "RAC + ZStandard".
   - All other values are reserved.
 
@@ -515,7 +517,7 @@
 ignored, other than deriving the `Secondary CRange`.
 
 
-## RAC + Brotli
+## RAC + LZ4
 
 TODO.
 
diff --git a/lib/rac/rac.go b/lib/rac/rac.go
index 093fa9e..e521586 100644
--- a/lib/rac/rac.go
+++ b/lib/rac/rac.go
@@ -83,7 +83,7 @@
 		case 1:
 			return "Zlib"
 		case 2:
-			return "Brotli"
+			return "LZ4"
 		case 4:
 			return "Zstandard"
 		}
@@ -98,7 +98,7 @@
 const (
 	CodecZeroes    = Codec(0x00 << 56)
 	CodecZlib      = Codec(0x01 << 56)
-	CodecBrotli    = Codec(0x02 << 56)
+	CodecLZ4       = Codec(0x02 << 56)
 	CodecZstandard = Codec(0x04 << 56)
 
 	codecMixBit     = Codec(1 << 62)