diff --git a/src/gl/data/gl_vertexbuffer.cpp b/src/gl/data/gl_vertexbuffer.cpp
index 637de85aa..05fd475c0 100644
--- a/src/gl/data/gl_vertexbuffer.cpp
+++ b/src/gl/data/gl_vertexbuffer.cpp
@@ -137,9 +137,9 @@ void FSimpleVertexBuffer::set(FSimpleVertex *verts, int count)
 //==========================================================================
 
 FFlatVertexBuffer::FFlatVertexBuffer(int width, int height)
-: FVertexBuffer(gl.buffermethod == BM_PERSISTENT)
+: FVertexBuffer(gl.buffermethod != BM_CLIENTARRAY)
 {
-	if (gl.buffermethod == BM_PERSISTENT)
+	if (gl.buffermethod != BM_CLIENTARRAY)
 	{
 		unsigned int bytesize = BUFFER_SIZE * sizeof(FFlatVertex);
 		glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
@@ -157,10 +157,10 @@ FFlatVertexBuffer::FFlatVertexBuffer(int width, int height)
 	vbo_shadowdata.Resize(mNumReserved);
 
 	// the first quad is reserved for handling coordinates through uniforms.
-	vbo_shadowdata[0].Set(1, 0, 0, 0, 0);
-	vbo_shadowdata[1].Set(2, 0, 0, 0, 0);
-	vbo_shadowdata[2].Set(3, 0, 0, 0, 0);
-	vbo_shadowdata[3].Set(4, 0, 0, 0, 0);
+	vbo_shadowdata[0].Set(0, 0, 0, 0, 0);
+	vbo_shadowdata[1].Set(1, 0, 0, 0, 0);
+	vbo_shadowdata[2].Set(2, 0, 0, 0, 0);
+	vbo_shadowdata[3].Set(3, 0, 0, 0, 0);
 
 	// and the second one for the fullscreen quad used for blend overlays.
 	vbo_shadowdata[4].Set(0, 0, 0, 0, 0);
diff --git a/src/gl/renderer/gl_quaddrawer.h b/src/gl/renderer/gl_quaddrawer.h
index 3fcca65c2..b9db60684 100644
--- a/src/gl/renderer/gl_quaddrawer.h
+++ b/src/gl/renderer/gl_quaddrawer.h
@@ -14,7 +14,7 @@ public:
 
 	FQuadDrawer()
 	{
-		if (gl.flags & RFL_QUADHACK)
+		if (gl.buffermethod == BM_DEFERRED)
 		{
 			p = buffer;
 		}
@@ -29,7 +29,7 @@ public:
 	}
 	void Render(int type)
 	{
-		if (gl.flags & RFL_QUADHACK)
+		if (gl.buffermethod == BM_DEFERRED)
 		{
 			DoRender(type);
 		}
diff --git a/src/gl/shaders/gl_shader.cpp b/src/gl/shaders/gl_shader.cpp
index c3f0f83da..67b9a2d6a 100644
--- a/src/gl/shaders/gl_shader.cpp
+++ b/src/gl/shaders/gl_shader.cpp
@@ -125,6 +125,10 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 			vp_comb = "#version 400 core\n#extension GL_ARB_shader_storage_buffer_object : require\n#define SHADER_STORAGE_LIGHTS\n";
 		}
 	}
+	//if (gl.buffermethod == BM_DEFERRED)
+	{
+		vp_comb << "#define USE_QUAD_DRAWER\n";
+	}
 
 	vp_comb << defines << i_data.GetString().GetChars();
 	FString fp_comb = vp_comb;
@@ -276,6 +280,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 	}
 
 	glUseProgram(hShader);
+	if (quadmode_index > 0) glUniform1i(quadmode_index, 0);
 
 	// set up other texture units (if needed by the shader)
 	for (int i = 2; i<16; i++)
diff --git a/src/gl/system/gl_interface.cpp b/src/gl/system/gl_interface.cpp
index 8c1e4cd9b..4d83ebec0 100644
--- a/src/gl/system/gl_interface.cpp
+++ b/src/gl/system/gl_interface.cpp
@@ -156,7 +156,15 @@ void gl_LoadExtensions()
 
 	gl.version = strtod(version, NULL) + 0.01f;
 
-	// Don't even start if it's lower than 3.0
+	bool iscore = false;
+	if (gl.version >= 3.2)
+	{
+		int v;
+		glGetIntegerv(GL_CONTEXT_PROFILE_MASK, &v);
+		iscore = !!(v & GL_CONTEXT_CORE_PROFILE_BIT);
+	}
+
+	// Don't even start if it's lower than 2.0 or no framebuffers are available
 	if ((gl.version < 2.0 || !CheckExtension("GL_EXT_framebuffer_object")) && gl.version < 3.0)
 	{
 		I_FatalError("Unsupported OpenGL version.\nAt least OpenGL 2.0 with framebuffer support is required to run " GAMENAME ".\n");
@@ -178,10 +186,10 @@ void gl_LoadExtensions()
 	if (gl.version > 3.0f && (gl.version >= 3.3f || CheckExtension("GL_ARB_uniform_buffer_object")))
 	{
 		gl.lightmethod = LM_DEFERRED;
-		// Only Apple requires the core profile for GL 3.x+.
-		// #ifdef __APPLE__
-		// gl.buffermethod = BM_DEFERRED;
-		// #endif
+		if (iscore)
+		{
+			gl.buffermethod = BM_DEFERRED;
+		}
 	}
 
 	if (CheckExtension("GL_ARB_texture_compression")) gl.flags |= RFL_TEXTURE_COMPRESSION;
@@ -256,7 +264,7 @@ void gl_LoadExtensions()
 	lm = Args->CheckValue("-buffermethod");
 	if (lm != NULL)
 	{
-		//if (!stricmp(lm, "deferred") && gl.buffermethod == BM_PERSISTENT) gl.buffermethod = BM_DEFERRED;
+		if (!stricmp(lm, "deferred") && gl.buffermethod == BM_PERSISTENT) gl.buffermethod = BM_DEFERRED;
 		if (!stricmp(lm, "clientarray")) gl.buffermethod = BM_CLIENTARRAY;
 	}
 
diff --git a/src/gl/system/gl_interface.h b/src/gl/system/gl_interface.h
index 9eca673f5..11b0573e5 100644
--- a/src/gl/system/gl_interface.h
+++ b/src/gl/system/gl_interface.h
@@ -25,8 +25,7 @@ enum RenderFlags
 	RFL_NO_DEPTHSTENCIL = 64,
 	RFL_NO_CLIP_PLANES = 128,
 
-	RFL_INVALIDATE_BUFFER = 256,
-	RFL_QUADHACK = 512
+	RFL_INVALIDATE_BUFFER = 256
 };
 
 enum TexMode
diff --git a/wadsrc/static/shaders/glsl/main.vp b/wadsrc/static/shaders/glsl/main.vp
index 281c509d3..a2c1bac5b 100644
--- a/wadsrc/static/shaders/glsl/main.vp
+++ b/wadsrc/static/shaders/glsl/main.vp
@@ -15,6 +15,7 @@ void main()
 {
 	vec2 parmTexCoord;
 	vec4 parmPosition;
+	
 	#ifndef USE_QUAD_DRAWER
 		parmTexCoord = aTexCoord;
 		parmPosition = aPosition;
@@ -26,8 +27,8 @@ void main()
 		}
 		else
 		{
-			parmPosition = uQuadVertices[int(aPosition.x)].st;
-			parmTexCoord = uQuadTexCoords[int(aPosition.x)];
+			parmPosition = uQuadVertices[int(aPosition.x)];
+			parmTexCoord = uQuadTexCoords[int(aPosition.x)].st;
 		}
 	#endif
 	
@@ -67,13 +68,7 @@ void main()
 	#endif
 	
 	gl_Position = ProjectionMatrix * eyeCoordPos;
-	
-    #if defined __GLSL_CG_DATA_TYPES && defined GLSL12_COMPATIBILE
-		gl_ClipVertex = eyeCoordPos;
-	#endif
-	
-	
-	
+		
 	if (uClipHeightDirection != 0.0) // clip planes used for reflective flats
 	{
 		gl_ClipDistance[0] = (worldcoord.y - uClipHeight) * uClipHeightDirection;