diff --git a/content/canvas/src/WebGLContextGL.cpp b/content/canvas/src/WebGLContextGL.cpp
index 927a88824e60..354cec2389ba 100644
--- a/content/canvas/src/WebGLContextGL.cpp
+++ b/content/canvas/src/WebGLContextGL.cpp
@@ -2319,15 +2319,15 @@ WebGLContext::ReadPixels(GLint x, GLint y, GLsizei width,
     MakeContextCurrent();
 
     if (mBoundFramebuffer) {
+        // prevent readback of arbitrary video memory through uninitialized renderbuffers!
+        if (!mBoundFramebuffer->CheckAndInitializeAttachments())
+            return ErrorInvalidFramebufferOperation("readPixels: incomplete framebuffer");
+
         GLenum readPlaneBits = LOCAL_GL_COLOR_BUFFER_BIT;
         if (!mBoundFramebuffer->HasCompletePlanes(readPlaneBits)) {
             return ErrorInvalidOperation("readPixels: Read source attachment doesn't have the"
                                          " correct color/depth/stencil type.");
         }
-
-        // prevent readback of arbitrary video memory through uninitialized renderbuffers!
-        if (!mBoundFramebuffer->CheckAndInitializeAttachments())
-            return ErrorInvalidFramebufferOperation("readPixels: incomplete framebuffer");
     }
     // Now that the errors are out of the way, on to actually reading