diff --git a/.devcontainer/Dockerfile b/.devcontainer/Dockerfile
index 2d4e600..27066a0 100644
--- a/.devcontainer/Dockerfile
+++ b/.devcontainer/Dockerfile
@@ -20,7 +20,7 @@ ADD https://github.com/einar-saukas/ZX0.git /zx0
 RUN cd /zx0/src/ \
 	&& gcc -O2 -o zx0 zx0.c optimize.c compress.c memory.c \
 	&& gcc -O2 -o dzx0 dzx0.c
-ADD https://www.boriel.com/files/zxb/zxbasic-1.18.3-linux64.tar.gz .
+ADD https://www.boriel.com/files/zxb/zxbasic-1.18.4-linux64.tar.gz .
 RUN tar xf zxbasic*
 ADD https://github.com/Mastodon-/inpaws.git /inpaws
 RUN cd /inpaws/ \
diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
index 9600cc9..c2d4bbe 100644
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -2,7 +2,7 @@
 	"name": "ZX Spectrum dev tools",
 	//"build": { "dockerfile": "Dockerfile" },
 	// The Dockerfile takes an age to build due to z88dk, so pull from prebuilt:
-	"image": "boarstone.mcphail.uk/mcphail/speccydev:v3.0",
+	"image": "boarstone.mcphail.uk/mcphail/speccydev:v4.0",
 	"remoteUser": "ubuntu",
 	"runArgs": [
 		"--network=host"
diff --git a/README.md b/README.md
index 80f19c5..2399480 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# Development tools for the ZX Spectrum v3.0
+# Development tools for the ZX Spectrum v4.0
 
 The Dockerfile is the basis of the devcontainer and can be changed to add or remove tools. It will take a long time to build locally, so by default the devcontainer will pull a prebuilt version. Edit `.devcontainer/devcontainer.json` if you would rather build your own.
 
@@ -29,7 +29,7 @@ The devcontainer contains:
     - tzxlist
 - zx0 (binary compressor)
 - dzx0 (binary decompressor)
-- ZX BASIC (aka Boriel BASIC) version 1.18.3
+- ZX BASIC (aka Boriel BASIC) version 1.18.4
     - zxbc (BASIC compiler)
     - zxbasm (assembler)
     - zxbpp (preprocessor)
@@ -62,9 +62,9 @@ Several useful VSCode extentsions will be installed, including a Z80 assembly la
 
 Thanks to the many authors of these wonderful tools and extensions; to think what we could have made with these in 1985!
 
-## Breaking changes from v2.x
+## Breaking changes from v3.x
 
-Boriel BASIC (zxbasic) has been updated. This version corrects a bug when referencing array data from assembly language. Code reliant on the old, faulty, behaviour may break.
+Boriel BASIC (zxbasic) has been updated. There have been further bug fixes to array referencing which may break old code reliant on previous behaviour.
 
 ## New additions from v2.x