diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index bdd0867b9..358c9fe7f 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -90,6 +90,7 @@ void FRenderState::Reset()
 	stSrcBlend = stDstBlend = -1;
 	stBlendEquation = -1;
 	stAlphaThreshold = -1.f;
+	mLastDepthClamp = true;
 }
 
 //==========================================================================
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index b30d7920f..8c3b60772 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -63,6 +63,7 @@ class FRenderState
 	float mInterpolationFactor;
 	float mClipHeightTop, mClipHeightBottom;
 	float mShaderTimer;
+	bool mLastDepthClamp;
 
 	FVertexBuffer *mVertexBuffer, *mCurrentVertexBuffer;
 	FStateVec4 mColor;
@@ -309,6 +310,16 @@ public:
 		}
 	}
 
+	// This wraps the depth clamp setting because we frequently need to read it which OpenGL is not particularly performant at...
+	bool SetDepthClamp(bool on)
+	{
+		bool res = mLastDepthClamp;
+		if (!on) glDisable(GL_DEPTH_CLAMP);
+		else glEnable(GL_DEPTH_CLAMP);
+		mLastDepthClamp = on;
+		return res;
+	}
+
 	void Set2DMode(bool on)
 	{
 		m2D = on;
diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index 02e7747bc..eba8b4d06 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -633,8 +633,7 @@ void GLSkyboxPortal::DrawContents()
 
 	PlaneMirrorMode=0;
 
-	glDisable(GL_DEPTH_CLAMP);
-
+	bool oldclamp = gl_RenderState.SetDepthClamp(false);
 	viewx = origin->PrevX + FixedMul(r_TicFrac, origin->x - origin->PrevX);
 	viewy = origin->PrevY + FixedMul(r_TicFrac, origin->y - origin->PrevY);
 	viewz = origin->PrevZ + FixedMul(r_TicFrac, origin->z - origin->PrevZ);
@@ -663,7 +662,7 @@ void GLSkyboxPortal::DrawContents()
 	GLRenderer->DrawScene();
 	origin->flags&=~MF_JUSTHIT;
 	inskybox=false;
-	glEnable(GL_DEPTH_CLAMP);
+	gl_RenderState.SetDepthClamp(oldclamp);
 	skyboxrecursion--;
 
 	PlaneMirrorMode=old_pm;
diff --git a/src/gl/scene/gl_skydome.cpp b/src/gl/scene/gl_skydome.cpp
index a6ee502d5..f431e06a6 100644
--- a/src/gl/scene/gl_skydome.cpp
+++ b/src/gl/scene/gl_skydome.cpp
@@ -475,6 +475,7 @@ void GLSkyPortal::DrawContents()
 	gl_RenderState.EnableFog(false);
 	gl_RenderState.AlphaFunc(GL_GEQUAL, 0.f);
 	gl_RenderState.BlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+	bool oldClamp = gl_RenderState.SetDepthClamp(true);
 
 	gl_MatrixStack.Push(gl_RenderState.mViewMatrix);
 	GLRenderer->SetupView(0, 0, 0, viewangle, !!(MirrorFlag&1), !!(PlaneMirrorFlag&1));
@@ -519,5 +520,6 @@ void GLSkyPortal::DrawContents()
 	gl_MatrixStack.Pop(gl_RenderState.mViewMatrix);
 	gl_RenderState.ApplyMatrices();
 	glset.lightmode = oldlightmode;
+	gl_RenderState.SetDepthClamp(oldClamp);
 }