diff --git a/sdk/tests/conformance2/renderbuffers/readbuffer.html b/sdk/tests/conformance2/renderbuffers/readbuffer.html
index 56bfd656a..57a0319d8 100644
--- a/sdk/tests/conformance2/renderbuffers/readbuffer.html
+++ b/sdk/tests/conformance2/renderbuffers/readbuffer.html
@@ -75,11 +75,16 @@
   gl.readBuffer(gl.COLOR_ATTACHMENT0);
   wtu.glErrorShouldBe(gl, gl.NO_ERROR,
       "calling readBuffer with GL_COLOR_ATTACHMENT0 on fbo should succeed.");
+  gl.readBuffer(gl.COLOR_ATTACHMENT0 - 1);
+  wtu.glErrorShouldBe(gl, gl.INVALID_ENUM,
+      "calling readBuffer with an enum below GL_COLOR_ATTACHMENT0 on fbo should generate INVALID_ENUM.");
+  shouldBe('gl.getParameter(gl.READ_BUFFER)', 'gl.COLOR_ATTACHMENT0');
 
   var maxColorAttachments = gl.getParameter(gl.MAX_COLOR_ATTACHMENTS);
   gl.readBuffer(gl.COLOR_ATTACHMENT0 + maxColorAttachments);
   wtu.glErrorShouldBe(gl, gl.INVALID_OPERATION,
       "calling readBuffer with GL_COLOR_ATTACHMENTi that exceeds MAX_COLOR_ATTACHMENT on fbo should generate INVALID_OPERATION.");
+  shouldBe('gl.getParameter(gl.READ_BUFFER)', 'gl.COLOR_ATTACHMENT0');
   gl.readBuffer(gl.COLOR_ATTACHMENT1);
   wtu.glErrorShouldBe(gl, gl.NO_ERROR,
       "calling readBuffer with GL_COLOR_ATTACHMENT1 on the fbo should succeed.");