diff --git a/install/gl/shadowmap_vp.glsl b/install/gl/shadowmap_vp.glsl
index 8238e2baa4..91bdaaa1e7 100644
--- a/install/gl/shadowmap_vp.glsl
+++ b/install/gl/shadowmap_vp.glsl
@@ -12,6 +12,7 @@ uniform vec4 u_DiffuseTextureMatrix[2];
 // The final diffuse texture coordinate at this vertex
 varying vec2 var_TexDiffuse;
 
+// The modelview matrices for each of the 6 cube map faces
 const mat3 cubicTransformations[6] = mat3[6]
 (
     mat3(0,  0, -1,
@@ -39,6 +40,17 @@ const mat3 cubicTransformations[6] = mat3[6]
           0,  0,  1)
 );
 
+// These 4 clip planes are 45 degrees planes passing the origin (opening towards negative z)
+// bounding the view frustum of a point light at 0,0,0
+const float clipEps = 0e-2;
+const vec4 ClipPlanes[4] = vec4[4]
+(
+    vec4(1, 0, -1, clipEps),
+    vec4(-1, 0, -1, clipEps),
+    vec4(0, 1, -1, clipEps),
+    vec4(0, -1, -1, clipEps)
+);
+
 void main()
 {
     // Transform the model vertex to world space, then subtract the light origin
@@ -46,10 +58,20 @@ void main()
     vec4 lightSpacePos = u_ObjectTransform * attr_Position;
     lightSpacePos.xyz -= u_LightOrigin;
 
+    // Render the vertex 6 times, once for each cubemap face (gl_InstanceID = [0..5])
+    // This is just a rotation, no scaling or projection involved
     vec4 fragPos = vec4(cubicTransformations[gl_InstanceID] * lightSpacePos.xyz, 1);
 
     gl_Position.x = fragPos.x / 6 + fragPos.z * 5/6 - fragPos.z / 3 * gl_InstanceID;
     gl_Position.y = fragPos.y;
     gl_Position.z = -fragPos.z - 2;
     gl_Position.w = -fragPos.z;
+
+    // To clip the vertices outside the view frustum, calculate its clip distance
+    // every fragment with a distance < 0 will be discarded
+    // This relies on the GL_CLIP_DISTANCE0-3 flags activated in the renderer code
+    gl_ClipDistance[0] = dot(fragPos, ClipPlanes[0]);
+    gl_ClipDistance[1] = dot(fragPos, ClipPlanes[1]);
+    gl_ClipDistance[2] = dot(fragPos, ClipPlanes[2]);
+    gl_ClipDistance[3] = dot(fragPos, ClipPlanes[3]);
 }
diff --git a/radiantcore/rendersystem/backend/LightingModeRenderer.cpp b/radiantcore/rendersystem/backend/LightingModeRenderer.cpp
index d9ffeffbfd..b2f13c35ad 100644
--- a/radiantcore/rendersystem/backend/LightingModeRenderer.cpp
+++ b/radiantcore/rendersystem/backend/LightingModeRenderer.cpp
@@ -99,16 +99,18 @@ IRenderResult::Ptr LightingModeRenderer::render(RenderStateFlags globalFlagsMask
     glDepthFunc(GL_LEQUAL);
     current.setDepthFunc(GL_LEQUAL);
 
-#if 1
     glEnable(GL_DEPTH_TEST);
     current.setRenderFlag(RENDER_DEPTHTEST);
+
     glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
     current.setRenderFlag(RENDER_FILL);
-#endif
-#if 0
-    glPolygonOffset(0, 0);
-    glEnable(GL_POLYGON_OFFSET_FILL);
-#endif
+
+    // Enable the 4 clip planes, they are used in the vertex shader
+    glEnable(GL_CLIP_DISTANCE0);
+    glEnable(GL_CLIP_DISTANCE1);
+    glEnable(GL_CLIP_DISTANCE2);
+    glEnable(GL_CLIP_DISTANCE3);
+
     // Render a single light to the shadow map buffer
     for (auto& interactionList : interactionLists)
     {
@@ -122,16 +124,17 @@ IRenderResult::Ptr LightingModeRenderer::render(RenderStateFlags globalFlagsMask
     _shadowMapFbo->unbind();
     _shadowMapProgram->disable();
 
+    glDisable(GL_CLIP_DISTANCE3);
+    glDisable(GL_CLIP_DISTANCE2);
+    glDisable(GL_CLIP_DISTANCE1);
+    glDisable(GL_CLIP_DISTANCE0);
+
     // Restore view port
     glViewport(previousViewport[0], previousViewport[1], previousViewport[2], previousViewport[3]);
 
-#if 0
-    glDisable(GL_POLYGON_OFFSET_FILL);
-#endif
-#if 1
     glDisable(GL_DEPTH_TEST);
     current.clearRenderFlag(RENDER_DEPTHTEST);
-#endif
+
     // Load the model view & projection matrix for the main scene
     setupViewMatrices(view);