diff --git a/src/gl/renderer/gl_postprocess.cpp b/src/gl/renderer/gl_postprocess.cpp
index f89776d63a..3b94fd8cc1 100644
--- a/src/gl/renderer/gl_postprocess.cpp
+++ b/src/gl/renderer/gl_postprocess.cpp
@@ -137,9 +137,6 @@ void FGLRenderer::PostProcessScene()
 
 void FGLRenderer::AmbientOccludeScene()
 {
-	if (!gl_ssao || !FGLRenderBuffers::IsEnabled())
-		return;
-
 	FGLDebug::PushGroup("AmbientOccludeScene");
 
 	FGLPostProcessState savedState;
@@ -226,20 +223,27 @@ void FGLRenderer::AmbientOccludeScene()
 	RenderScreenQuad();
 
 	// Add SSAO back to scene texture:
-	mBuffers->BindSceneFB();
+	mBuffers->BindSceneFB(false);
+	GLenum buffers[] = { GL_COLOR_ATTACHMENT0 };
+	glDrawBuffers(1, buffers);
 	glViewport(mSceneViewport.left, mSceneViewport.top, mSceneViewport.width, mSceneViewport.height);
 	glEnable(GL_BLEND);
 	glBlendEquation(GL_FUNC_ADD);
 	if (gl_ssao_debug)
 		glBlendFunc(GL_ONE, GL_ZERO);
 	else
-		glBlendFunc(GL_ZERO, GL_SRC_COLOR);
+		glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 	glActiveTexture(GL_TEXTURE0);
 	glBindTexture(GL_TEXTURE_2D, mBuffers->AmbientTexture1);
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
-	mSSAOCombineShader->Bind();
-	mSSAOCombineShader->AODepthTexture.Set(0);
+	mBuffers->BindSceneDataTexture(1);
+	mSSAOCombineShader->Bind(multisample);
+	mSSAOCombineShader->AODepthTexture[multisample].Set(0);
+	mSSAOCombineShader->SceneDataTexture[multisample].Set(1);
+	if (multisample) mSSAOCombineShader->SampleCount[multisample].Set(gl_multisample);
+	mSSAOCombineShader->Scale[multisample].Set(mBuffers->AmbientWidth * 2.0f / (float)mScreenViewport.width, mBuffers->AmbientHeight * 2.0f / (float)mScreenViewport.height);
+	mSSAOCombineShader->Offset[multisample].Set(mSceneViewport.left / (float)mScreenViewport.width, mSceneViewport.top / (float)mScreenViewport.height);
 	RenderScreenQuad();
 
 	FGLDebug::PopGroup();
diff --git a/src/gl/renderer/gl_renderer.cpp b/src/gl/renderer/gl_renderer.cpp
index befa330e96..368db63d2e 100644
--- a/src/gl/renderer/gl_renderer.cpp
+++ b/src/gl/renderer/gl_renderer.cpp
@@ -323,7 +323,7 @@ void FGLRenderer::Begin2D()
 	if (mBuffers->Setup(mScreenViewport.width, mScreenViewport.height, mSceneViewport.width, mSceneViewport.height))
 	{
 		if (mDrawingScene2D)
-			mBuffers->BindSceneFB();
+			mBuffers->BindSceneFB(false);
 		else
 			mBuffers->BindCurrentFB();
 	}
diff --git a/src/gl/scene/gl_scene.cpp b/src/gl/scene/gl_scene.cpp
index a50fe87f8b..6a8c9a11a1 100644
--- a/src/gl/scene/gl_scene.cpp
+++ b/src/gl/scene/gl_scene.cpp
@@ -158,7 +158,11 @@ void FGLRenderer::Set3DViewport(bool mainview)
 {
 	if (mainview && mBuffers->Setup(mScreenViewport.width, mScreenViewport.height, mSceneViewport.width, mSceneViewport.height))
 	{
-		mBuffers->BindSceneFB();
+		mBuffers->BindSceneFB(gl_ssao);
+		GLenum buffers[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
+		glDrawBuffers(gl_ssao ? 2 : 1, buffers);
+		gl_RenderState.SetPassType(gl_ssao ? GBUFFER_PASS : NORMAL_PASS);
+		gl_RenderState.Apply();
 	}
 
 	// Always clear all buffers with scissor test disabled.
@@ -491,7 +495,13 @@ void FGLRenderer::DrawScene(int drawmode)
 
 	RenderScene(recursion);
 
-	AmbientOccludeScene();
+	bool applySSAO = gl_ssao && FGLRenderBuffers::IsEnabled() && drawmode != DM_PORTAL;
+	if (applySSAO)
+	{
+		AmbientOccludeScene();
+		gl_RenderState.SetPassType(GBUFFER_PASS);
+		gl_RenderState.Apply();
+	}
 
 	// Handle all portals after rendering the opaque objects but before
 	// doing all translucent stuff
@@ -499,6 +509,15 @@ void FGLRenderer::DrawScene(int drawmode)
 	GLPortal::EndFrame();
 	recursion--;
 	RenderTranslucent();
+
+	if (applySSAO)
+	{
+		mBuffers->BindSceneFB(true);
+		GLenum buffers[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
+		glDrawBuffers(2, buffers);
+		gl_RenderState.SetPassType(NORMAL_PASS);
+		gl_RenderState.Apply();
+	}
 }
 
 
diff --git a/src/gl/shaders/gl_ambientshader.cpp b/src/gl/shaders/gl_ambientshader.cpp
index 3fbd034348..4fa5b0e019 100644
--- a/src/gl/shaders/gl_ambientshader.cpp
+++ b/src/gl/shaders/gl_ambientshader.cpp
@@ -120,16 +120,21 @@ void FDepthBlurShader::Bind(bool vertical)
 	shader.Bind();
 }
 
-void FSSAOCombineShader::Bind()
+void FSSAOCombineShader::Bind(bool multisample)
 {
-	if (!mShader)
+	auto &shader = mShader[multisample];
+	if (!shader)
 	{
-		mShader.Compile(FShaderProgram::Vertex, "shaders/glsl/screenquad.vp", "", 330);
-		mShader.Compile(FShaderProgram::Fragment, "shaders/glsl/ssaocombine.fp", "", 330);
-		mShader.SetFragDataLocation(0, "FragColor");
-		mShader.Link("shaders/glsl/ssaocombine");
-		mShader.SetAttribLocation(0, "PositionInProjection");
-		AODepthTexture.Init(mShader, "AODepthTexture");
+		shader.Compile(FShaderProgram::Vertex, "shaders/glsl/screenquad.vp", "", 330);
+		shader.Compile(FShaderProgram::Fragment, "shaders/glsl/ssaocombine.fp", multisample ? "#define MULTISAMPLE\n" : "", 330);
+		shader.SetFragDataLocation(0, "FragColor");
+		shader.Link("shaders/glsl/ssaocombine");
+		shader.SetAttribLocation(0, "PositionInProjection");
+		AODepthTexture[multisample].Init(shader, "AODepthTexture");
+		SceneDataTexture[multisample].Init(shader, "SceneDataTexture");
+		SampleCount[multisample].Init(shader, "SampleCount");
+		Scale[multisample].Init(shader, "Scale");
+		Offset[multisample].Init(shader, "Offset");
 	}
-	mShader.Bind();
+	shader.Bind();
 }
diff --git a/src/gl/shaders/gl_ambientshader.h b/src/gl/shaders/gl_ambientshader.h
index 9c97791ba8..f36b10625e 100644
--- a/src/gl/shaders/gl_ambientshader.h
+++ b/src/gl/shaders/gl_ambientshader.h
@@ -59,12 +59,16 @@ private:
 class FSSAOCombineShader
 {
 public:
-	void Bind();
+	void Bind(bool multisample);
 
-	FBufferedUniformSampler AODepthTexture;
+	FBufferedUniformSampler AODepthTexture[2];
+	FBufferedUniformSampler SceneDataTexture[2];
+	FBufferedUniform1i SampleCount[2];
+	FBufferedUniform2f Scale[2];
+	FBufferedUniform2f Offset[2];
 
 private:
-	FShaderProgram mShader;
+	FShaderProgram mShader[2];
 };
 
 #endif
\ No newline at end of file
diff --git a/src/gl/system/gl_cvars.h b/src/gl/system/gl_cvars.h
index 4cda3657de..97bd0b46c6 100644
--- a/src/gl/system/gl_cvars.h
+++ b/src/gl/system/gl_cvars.h
@@ -50,6 +50,12 @@ EXTERN_CVAR(Bool, gl_lens)
 EXTERN_CVAR(Float, gl_lens_k)
 EXTERN_CVAR(Float, gl_lens_kcube)
 EXTERN_CVAR(Float, gl_lens_chromatic)
+EXTERN_CVAR(Bool, gl_ssao)
+EXTERN_CVAR(Float, gl_ssao_strength)
+EXTERN_CVAR(Bool, gl_ssao_debug)
+EXTERN_CVAR(Float, gl_ssao_bias)
+EXTERN_CVAR(Float, gl_ssao_radius)
+EXTERN_CVAR(Float, gl_ssao_blur_amount)
 
 EXTERN_CVAR(Int, gl_debug_level)
 EXTERN_CVAR(Bool, gl_debug_breakpoint)
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index 4d3531f010..0d2b419c15 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -233,6 +233,32 @@ vec4 applyFog(vec4 frag, float fogfactor)
 	return vec4(mix(uFogColor.rgb, frag.rgb, fogfactor), frag.a);
 }
 
+//===========================================================================
+//
+// The color of the fragment if it is fully occluded by ambient lighting
+//
+//===========================================================================
+
+vec3 AmbientOcclusionColor()
+{
+	float fogdist;
+	float fogfactor;
+			
+	//
+	// calculate fog factor
+	//
+	if (uFogEnabled == -1) 
+	{
+		fogdist = pixelpos.w;
+	}
+	else 
+	{
+		fogdist = max(16.0, length(pixelpos.xyz));
+	}
+	fogfactor = exp2 (uFogDensity * fogdist);
+			
+	return mix(uFogColor.rgb, vec3(0.0), fogfactor);
+}
 
 //===========================================================================
 //
@@ -349,7 +375,7 @@ void main()
 	}
 	FragColor = frag;
 #ifdef GBUFFER_PASS
-	FragData = vec4(uFogColor.rgb, 1.0);
+	FragData = vec4(AmbientOcclusionColor(), 1.0);
 #endif
 }
 
diff --git a/wadsrc/static/shaders/glsl/ssaocombine.fp b/wadsrc/static/shaders/glsl/ssaocombine.fp
index 21fdff1024..7cd0962763 100644
--- a/wadsrc/static/shaders/glsl/ssaocombine.fp
+++ b/wadsrc/static/shaders/glsl/ssaocombine.fp
@@ -4,8 +4,35 @@ out vec4 FragColor;
 
 uniform sampler2D AODepthTexture;
 
+#if defined(MULTISAMPLE)
+uniform sampler2DMS SceneDataTexture;
+uniform int SampleCount;
+#else
+uniform sampler2D SceneDataTexture;
+#endif
+
+uniform vec2 Scale;
+uniform vec2 Offset;
+
 void main()
 {
+	vec2 uv = Offset + TexCoord * Scale;
+#if defined(MULTISAMPLE)
+	ivec2 texSize = textureSize(SceneDataTexture);
+#else
+	ivec2 texSize = textureSize(SceneDataTexture, 0);
+#endif
+	ivec2 ipos = ivec2(max(floor(uv * vec2(texSize) - 0.75), vec2(0.0)));
+
+#if defined(MULTISAMPLE)
+	vec3 fogColor = vec3(0.0);
+	for (int i = 0; i < SampleCount; i++)
+		fogColor += texelFetch(SceneDataTexture, ipos, i).rgb;
+	fogColor /= float(SampleCount);
+#else
+	vec3 fogColor = texelFetch(SceneDataTexture, ipos, 0).rgb;
+#endif
+
 	float attenutation = texture(AODepthTexture, TexCoord).x;
-	FragColor = vec4(attenutation, attenutation, attenutation, 0.0);
+	FragColor = vec4(fogColor, 1.0 - attenutation);
 }