diff --git a/emsdk.py b/emsdk.py
index 69135da..c6d1f55 100644
--- a/emsdk.py
+++ b/emsdk.py
@@ -2182,6 +2182,17 @@
   if extra_release_tag:
     tags.append(extra_release_tag)
 
+  # Adds the currently installed SDK version, which might be a custom
+  # version.  This means it will show up in `list` and work with
+  # `construct_env`
+  version_file = sdk_path(os.path.join('upstream', '.emsdk_version'))
+  if os.path.exists(version_file):
+    with open(version_file) as f:
+      version = f.read()
+    version = version.split('-')[2]
+    if version not in tags:
+      tags.append(version)
+
   return tags, tags_fastcomp
 
 
diff --git a/scripts/test.sh b/scripts/test.sh
index 73c0d42..473dbb1 100755
--- a/scripts/test.sh
+++ b/scripts/test.sh
@@ -5,10 +5,19 @@
 set -x
 set -e
 
+# Test that arbitrary (non-released) versions can be installed and
+# activated.
+./emsdk install sdk-upstream-5c776e6a91c0cb8edafca16a652ee1ee48f4f6d2
+./emsdk activate sdk-upstream-5c776e6a91c0cb8edafca16a652ee1ee48f4f6d2
+source ./emsdk_env.sh
+which emcc
+emcc -v
+
 ./emsdk install latest
 ./emsdk activate latest
 source ./emsdk_env.sh --build=Release
 # On mac and windows python3 should be in the path and point to the
 # bundled version.
 which python3
+which emcc
 emcc -v