--- a/content/canvas/src/WebGLContextGL.cpp
+++ b/content/canvas/src/WebGLContextGL.cpp
@@ -891,16 +891,20 @@ WebGLContext::CopyTexSubImage2D_base(Web
                                      bool sub)
 {
     const WebGLRectangleObject *framebufferRect = FramebufferRectangleObject();
     WebGLsizei framebufferWidth = framebufferRect ? framebufferRect->Width() : 0;
     WebGLsizei framebufferHeight = framebufferRect ? framebufferRect->Height() : 0;
 
     const char *info = sub ? "copyTexSubImage2D" : "copyTexImage2D";
 
+    if (!ValidateLevelWidthHeightForTarget(target, level, width, height, info)) {
+        return;
+    }
+
     MakeContextCurrent();
 
     WebGLTexture *tex = activeBoundTextureForTarget(target);
 
     if (!tex)
         return ErrorInvalidOperation("%s: no texture is bound to this target");
 
     if (CanvasUtils::CheckSaneSubrectSize(x, y, width, height, framebufferWidth, framebufferHeight)) {