diff --git a/src/render/rendergl3.cpp b/src/render/rendergl3.cpp
index 167ce03..cc21130 100644
--- a/src/render/rendergl3.cpp
+++ b/src/render/rendergl3.cpp
@@ -5,6 +5,7 @@
 //-----------------------------------------------------------------------------
 #include "solvespace.h"
 #include "gl3shader.h"
+#include <fstream>

 namespace SolveSpace {

@@ -679,10 +680,25 @@ void OpenGl3Renderer::Clear() {
 }

 std::shared_ptr<Pixmap> OpenGl3Renderer::ReadFrame() {
+    std::ofstream err("t:/solvespace-err.log");
+    err << std::hex;
+
     std::shared_ptr<Pixmap> pixmap =
         Pixmap::Create(Pixmap::Format::RGB, (size_t)camera.width, (size_t)camera.height);
+
+    err << "pregl\n";
+    for(GLenum e; (e = glGetError()) != GL_NO_ERROR;) {
+        err << e << '\n';
+    }
+
     glReadPixels(0, 0, (int)camera.width, (int)camera.height,
                  GL_RGB, GL_UNSIGNED_BYTE, &pixmap->data[0]);
+
+    err << "postgl\n";
+    for(GLenum e; (e = glGetError()) != GL_NO_ERROR;) {
+        err << e << '\n';
+    }
+
     return pixmap;
 }