diff --git a/include/qbsp/qbsp.hh b/include/qbsp/qbsp.hh
index 31c97eea..69c927e0 100644
--- a/include/qbsp/qbsp.hh
+++ b/include/qbsp/qbsp.hh
@@ -117,6 +117,7 @@
 #define CFLAGS_WAS_ILLUSIONARY           (1U << 1) /* was illusionary, got changed to something else */
 #define CFLAGS_DETAIL_WALL  (1U << 2) /* don't clip world for func_detail_wall entities */
 #define CFLAGS_BMODEL_MIRROR_INSIDE		 (1U << 3) /* set "_mirrorinside" "1" on a bmodel to mirror faces for when the player is inside. */
+#define CFLAGS_NO_CLIPPING_SAME_TYPE     (1U << 4) /* Don't clip the same content type. mostly intended for CONTENTS_DETAIL_ILLUSIONARY */
 
 // Texture flags. Only TEX_SPECIAL is written to the .bsp.
 // Extended flags are written to a .texinfo file and read by the light tool
diff --git a/qbsp/brush.cc b/qbsp/brush.cc
index 4f94884f..69ad9470 100644
--- a/qbsp/brush.cc
+++ b/qbsp/brush.cc
@@ -1122,6 +1122,11 @@ Brush_LoadEntity(mapentity_t *dst, const mapentity_t *src, const int hullnum)
     if (atoi(ValueForKey(src, "_mirrorinside"))) {
         cflags |= CFLAGS_BMODEL_MIRROR_INSIDE;
     }
+    
+    /* _noclipfaces */
+    if (atoi(ValueForKey(src, "_noclipfaces"))) {
+        cflags |= CFLAGS_NO_CLIPPING_SAME_TYPE;
+    }
 
     const bool func_illusionary_visblocker =
         (0 == Q_strcasecmp(classname, "func_illusionary_visblocker"));
diff --git a/qbsp/csg4.cc b/qbsp/csg4.cc
index 8e73df37..2bc85d6e 100644
--- a/qbsp/csg4.cc
+++ b/qbsp/csg4.cc
@@ -624,6 +624,12 @@ CSGFaces(const mapentity_t *entity)
                 /* CONTENTS_DETAIL_FENCE never clips anything but itself */
                 continue;
             }
+            
+            if (clipbrush->contents == brush->contents
+                && (clipbrush->cflags & CFLAGS_NO_CLIPPING_SAME_TYPE)) {
+                /* _noclipfaces key */
+                continue;
+            }
 
             /* check bounding box first */
             for (i = 0; i < 3; i++) {