diff --git a/Makefile b/Makefile
index 3118737b..4c1c7f8a 100644
--- a/Makefile
+++ b/Makefile
@@ -41,11 +41,15 @@ ifneq ($(unstripped),)
     DEPLOY_DIR := $(DEPLOY_DIR)_unstripped
 endif
 
-protonsdk_version := 0.20210126.1-1
 CONFIGURE_CMD := ../proton/configure.sh \
-	--proton-sdk-image=registry.gitlab.steamos.cloud/proton/soldier/sdk:$(protonsdk_version) \
 	--build-name="$(_build_name)"
 
+ifneq ($(protonsdk_version),)
+CONFIGURE_CMD += --proton-sdk-image=registry.gitlab.steamos.cloud/proton/soldier/sdk:$(protonsdk_version)
+else
+protonsdk_version := $(shell grep '^arg_protonsdk_image=' configure.sh|xargs echo|cut -d: -f2)
+endif
+
 
 all: help
 
diff --git a/README.md b/README.md
index a46e01df..217971f7 100644
--- a/README.md
+++ b/README.md
@@ -172,19 +172,22 @@ After setting up the build machine, it is time to run the configure script
 which will generate the Makefile to build your project. Run these steps. You
 may of course use whatever paths you like.
 
-To build Proton within the Steam Runtime (see `Makefile` for the correct
-protonsdk_version value to use):
+To build Proton using the official Proton SDK images:
 
         mkdir build/
         cd build
-        ../proton/configure.sh --proton-sdk-image=registry.gitlab.steamos.cloud/proton/soldier/sdk:$(protonsdk_version)
+        ../proton/configure.sh
 
-Or, if you are building without the Steam runtime, then instead use:
+If you want to build with a custom version of the Proton SDK images, then instead use:
+
+        ../proton/configure.sh --proton-sdk-image=registry.gitlab.steamos.cloud/proton/soldier/sdk:<version>
+
+Or, if you want to build without the Proton SDK, then instead use:
 
         ../proton/configure.sh --no-proton-sdk
 
 **Tip**: If you are building without the Steam runtime, you should now run
-`make obj-wine64/Makefile obj-wine32/Makefile` and check the files
+`make wine-configure64 wine-configure32` and check the files
 `obj-wine64/config.log` and `obj-wine32/config.log` for missing packages.
 Search for `won't be supported`. A couple of missing packages are normal:
 `opencv`, `oss`. More than that may indicate a problem.  Please see your
diff --git a/configure.sh b/configure.sh
index eae6605b..eee3dbe2 100755
--- a/configure.sh
+++ b/configure.sh
@@ -97,7 +97,7 @@ function configure() {
 #
 
 arg_steamrt="soldier"
-arg_protonsdk_image=""
+arg_protonsdk_image="registry.gitlab.steamos.cloud/proton/soldier/sdk:0.20210126.1-1"
 arg_no_protonsdk=""
 arg_build_name=""
 arg_docker_opts=""
@@ -208,7 +208,6 @@ usage() {
   exit 1;
 }
 
-[[ $# -gt 0 ]] || usage info
 parse_args "$@" || usage err
 [[ -z $arg_help ]] || usage info
 
diff --git a/docker/README.md b/docker/README.md
index a9583107..8668ee02 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -40,8 +40,8 @@ To update the official Proton SDK images:
    images and version them with the same tag as the Git tag.
 
 4) Once the images have been published, update the default
-   `protonsdk_version` version number in `Makefile` to use the newly
-   built images by default.
+   `arg_protonsdk_image` version number in `configure.sh` to use the
+   newly built images by default.
 
 Any change or addition to GPL-ed source first requires to update or add
 the corresponding source to <https://repo.steampowered.com/proton-sdk>.