diff --git a/Outputs/CRT/CRT.cpp b/Outputs/CRT/CRT.cpp
index 2c5969047..7905f02b3 100644
--- a/Outputs/CRT/CRT.cpp
+++ b/Outputs/CRT/CRT.cpp
@@ -69,7 +69,8 @@ CRT::CRT(unsigned int common_output_divisor) :
 	_common_output_divisor(common_output_divisor),
 	_is_writing_composite_run(false),
 	_delegate(nullptr),
-	_frames_since_last_delegate_call(0) {}
+	_frames_since_last_delegate_call(0),
+	_did_start_run(false) {}
 
 CRT::CRT(unsigned int cycles_per_line, unsigned int common_output_divisor, unsigned int height_of_display, ColourSpace colour_space, unsigned int colour_cycle_numerator, unsigned int colour_cycle_denominator, unsigned int buffer_depth) : CRT(common_output_divisor)
 {
@@ -186,9 +187,9 @@ void CRT::advance_cycles(unsigned int number_of_cycles, unsigned int source_divi
 		if(needs_endpoint)
 		{
 			if(
-				_openGL_output_builder->composite_output_run_has_room_for_vertices(_did_start_run ? 6 : 3) &&
-				!_openGL_output_builder->composite_output_buffer_is_full() &&
-				_is_writing_composite_run == _did_start_run)
+				_is_writing_composite_run == _did_start_run &&
+				_openGL_output_builder->composite_output_run_has_room_for_vertices(_did_start_run ? 3 : 6) &&
+				!_openGL_output_builder->composite_output_buffer_is_full())
 			{
 				uint8_t *next_run = _openGL_output_builder->get_next_output_run();
 				if(next_run)
diff --git a/Outputs/CRT/Internals/CRTOpenGL.cpp b/Outputs/CRT/Internals/CRTOpenGL.cpp
index cc000f45c..0dcd0e3c0 100644
--- a/Outputs/CRT/Internals/CRTOpenGL.cpp
+++ b/Outputs/CRT/Internals/CRTOpenGL.cpp
@@ -188,14 +188,6 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 
 		set_timing_uniforms();
 		set_colour_space_uniforms();
-
-		// This should return either an actual framebuffer number, if this is a target with a framebuffer intended for output,
-		// or 0 if no framebuffer is bound, in which case 0 is also what we want to supply to bind the implied framebuffer. So
-		// it works either way.
-//		glGetIntegerv(GL_FRAMEBUFFER_BINDING, (GLint *)&defaultFramebuffer);
-
-		// TODO: is this sustainable, cross-platform? If so, why store it at all?
-//		defaultFramebuffer = 0;
 	}
 
 	// determine how many lines are newly reclaimed; they'll need to be cleared
@@ -214,12 +206,6 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 	_drawn_source_buffer_data_pointer = _source_buffer_data_pointer;
 	_drawn_output_buffer_data_pointer = _output_buffer_data_pointer;
 
-	// drawing commands having been issued, reclaim the array buffer pointer
-//	glBindBuffer(GL_ARRAY_BUFFER, output_array_buffer);
-//
-//	glBindBuffer(GL_ARRAY_BUFFER, source_array_buffer);
-//	_source_buffer_data = (uint8_t *)glMapBufferRange(GL_ARRAY_BUFFER, 0, SourceVertexBufferDataSize, GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT | GL_MAP_FLUSH_EXPLICIT_BIT);
-
 	if(_fence != nullptr)
 	{
 		glClientWaitSync(_fence, GL_SYNC_FLUSH_COMMANDS_BIT, GL_TIMEOUT_IGNORED);
@@ -316,9 +302,6 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 
 			active_pipeline++;
 		}
-
-		// TODO: determine why the finish below is required
-//		glFinish();
 	}
 
 	// transfer to framebuffer
diff --git a/Outputs/CRT/Internals/CRTOpenGL.hpp b/Outputs/CRT/Internals/CRTOpenGL.hpp
index 903e7c501..ba0ec23ea 100644
--- a/Outputs/CRT/Internals/CRTOpenGL.hpp
+++ b/Outputs/CRT/Internals/CRTOpenGL.hpp
@@ -119,7 +119,7 @@ class OpenGLOutputBuilder {
 
 		inline bool composite_output_run_has_room_for_vertices(GLsizei vertices_to_write)
 		{
-			return _composite_src_output_y <= _cleared_composite_output_y + IntermediateBufferHeight - vertices_to_write * OutputVertexSize;
+			return _output_buffer_data_pointer <= _drawn_output_buffer_data_pointer + OutputVertexBufferDataSize - vertices_to_write * OutputVertexSize;
 		}
 
 		inline uint8_t *get_next_output_run()