diff --git a/sdk/tests/conformance/glsl/misc/00_test_list.txt b/sdk/tests/conformance/glsl/misc/00_test_list.txt
index c60310df14..00d373b212 100644
--- a/sdk/tests/conformance/glsl/misc/00_test_list.txt
+++ b/sdk/tests/conformance/glsl/misc/00_test_list.txt
@@ -41,6 +41,7 @@ shader-with-default-precision.vert.html
 shader-with-dfdx-no-ext.frag.html
 shader-with-dfdx.frag.html
 --min-version 1.0.2 shader-with-do-loop.html
+--min-version 1.0.4 shader-with-double-underscore.html
 shader-with-error-directive.html
 shader-with-explicit-int-cast.vert.html
 shader-with-float-return-value.frag.html
diff --git a/sdk/tests/conformance/glsl/misc/shader-with-double-underscore.html b/sdk/tests/conformance/glsl/misc/shader-with-double-underscore.html
new file mode 100644
index 0000000000..19b9e31a7d
--- /dev/null
+++ b/sdk/tests/conformance/glsl/misc/shader-with-double-underscore.html
@@ -0,0 +1,43 @@
+<!--
+Copyright (c) 2026 The Khronos Group Inc.
+Use of this source code is governed by an MIT-style license that can be
+found in the LICENSE.txt file.
+-->
+
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>WebGL GLSL Conformance Tests</title>
+<link rel="stylesheet" href="../../../resources/js-test-style.css"/>
+<link rel="stylesheet" href="../../../resources/glsl-feature-tests.css"/>
+<script src="../../../js/js-test-pre.js"></script>
+<script src="../../../js/webgl-test-utils.js"></script>
+<script src="../../../js/glsl-conformance-test.js"></script>
+</head>
+<body>
+<div id="description"></div>
+<div id="console"></div>
+<script id="vertexShader" type="text/something-not-javascript">
+// vertex shader that uses double-underscore in identifier should succeed
+attribute vec4 foo__bar;
+void main()
+{
+    gl_Position = foo__bar;
+}
+</script>
+<script id="fragmentShader" type="text/something-not-javascript">
+// fragment shader that uses double-underscore in identifier should succeed
+attribute vec4 foo__bar;
+void main()
+{
+    gl_FragColor = foo__bar;
+}
+</script>
+<script>
+"use strict";
+GLSLConformanceTester.runTest();
+var successfullyParsed = true;
+</script>
+</body>
+</html>
diff --git a/specs/latest/1.0/index.html b/specs/latest/1.0/index.html
index 6b126584f7..d38be38cfe 100644
--- a/specs/latest/1.0/index.html
+++ b/specs/latest/1.0/index.html
@@ -4668,6 +4668,16 @@ <h3><a name="CURRENT_PROGRAM_INVALIDATED">Current program invalidated upon unsuc
     </p>
 </div>
 
+
+<h3><a name="DOUBLE_UNDERSCORE_IN_SHADER_IDENTIFIERS">Double-Underscore in Shader Identifiers</a></h3>
+<p>
+    Identifiers in shaders may contain double-underscores, for example as in <code>"g__Foo"</code>.
+</p>
+<div class="note rationale">
+    To ensure robust portablility, implementations shall support this even if the underlying driver does not support this. (via e.g. mangling)
+</div>
+
+
 <!-- ======================================================================================================= -->
 
     <h2>References</h2>
