diff --git a/common/bspfile.cc b/common/bspfile.cc
index 94589140..0b69eb8a 100644
--- a/common/bspfile.cc
+++ b/common/bspfile.cc
@@ -70,6 +70,12 @@ struct gamedef_generic_t : public gamedef_t
 
     contentflags_t create_liquid_contents(const int32_t &, const int32_t &) const { throw std::bad_cast(); }
 
+    contentflags_t create_detail_illusionary_contents(const contentflags_t &original) const { throw std::bad_cast(); }
+
+    contentflags_t create_detail_fence_contents(const contentflags_t &original) const { throw std::bad_cast(); }
+
+    contentflags_t create_detail_solid_contents(const contentflags_t &original) const { throw std::bad_cast(); }
+
     bool contents_are_any_detail(const contentflags_t &) const { throw std::bad_cast(); }
 
     bool contents_are_detail_solid(const contentflags_t &contents) const { throw std::bad_cast(); }
@@ -213,6 +219,19 @@ struct gamedef_q1_like_t : public gamedef_t
         return {liquid_type, cflags};
     }
 
+    contentflags_t create_detail_illusionary_contents(const contentflags_t &original) const {
+        // ignore the original contents in Q1
+        return {0, CFLAGS_DETAIL_ILLUSIONARY};
+    }
+
+    contentflags_t create_detail_fence_contents(const contentflags_t &original) const {
+        return {0, CFLAGS_DETAIL_FENCE};
+    }
+
+    contentflags_t create_detail_solid_contents(const contentflags_t &original) const {
+        return {0, CFLAGS_DETAIL};
+    }
+
     bool contents_are_any_detail(const contentflags_t &contents) const
     {
         // in Q1, there are only CFLAGS_DETAIL, CFLAGS_DETAIL_ILLUSIONARY, or CFLAGS_DETAIL_FENCE
@@ -555,6 +574,26 @@ struct gamedef_q2_t : public gamedef_t
         }
     }
 
+    contentflags_t create_detail_illusionary_contents(const contentflags_t &original) const {
+        contentflags_t result = original;
+        result.native &= ~Q2_CONTENTS_SOLID;
+        result.native |= Q2_CONTENTS_MIST | Q2_CONTENTS_DETAIL;
+        return result;
+    }
+
+    contentflags_t create_detail_fence_contents(const contentflags_t &original) const {
+        contentflags_t result = original;
+        result.native &= ~Q2_CONTENTS_SOLID;
+        result.native |= (Q2_CONTENTS_WINDOW | Q2_CONTENTS_TRANSLUCENT | Q2_CONTENTS_DETAIL);
+        return result;
+    }
+
+    contentflags_t create_detail_solid_contents(const contentflags_t &original) const {
+        contentflags_t result = original;
+        result.native |= (Q2_CONTENTS_SOLID | Q2_CONTENTS_DETAIL);
+        return result;
+    }
+
     bool contents_are_any_detail(const contentflags_t &contents) const
     {
         return ((contents.native & Q2_CONTENTS_DETAIL) != 0);
@@ -562,20 +601,32 @@ struct gamedef_q2_t : public gamedef_t
 
     bool contents_are_detail_solid(const contentflags_t &contents) const
     {
-        // fixme-brushbsp: check native flag
-        return ((contents.extended & CFLAGS_DETAIL) != 0);
+        int32_t test = (Q2_CONTENTS_DETAIL|Q2_CONTENTS_SOLID);
+
+        return ((contents.native & test) == test);
     }
 
     bool contents_are_detail_fence(const contentflags_t &contents) const
     {
-        // fixme-brushbsp: check native flag
-        return ((contents.extended & CFLAGS_DETAIL_FENCE) != 0);
+        if (contents.native & Q2_CONTENTS_SOLID) {
+            return false;
+        }
+
+        int32_t test = (Q2_CONTENTS_DETAIL|Q2_CONTENTS_WINDOW);
+        return ((contents.native & test) == test);
     }
 
     bool contents_are_detail_illusionary(const contentflags_t &contents) const
     {
-        // fixme-brushbsp: check native flag
-        return ((contents.extended & CFLAGS_DETAIL_ILLUSIONARY) != 0);
+        if (contents.native & Q2_CONTENTS_SOLID) {
+            return false;
+        }
+
+        int32_t mist1_type = (Q2_CONTENTS_DETAIL|Q2_CONTENTS_MIST);
+        int32_t mist2_type = (Q2_CONTENTS_DETAIL|Q2_CONTENTS_AUX);
+
+        return ((contents.native & mist1_type) == mist1_type)
+            || ((contents.native & mist2_type) == mist2_type);
     }
 
     bool contents_are_empty(const contentflags_t &contents) const
@@ -740,6 +791,7 @@ struct gamedef_q2_t : public gamedef_t
         // FIXME: this is a bit of a hack, but this is because clip
         // and liquids and stuff are already handled *like* detail by
         // the compiler.
+        // fixme-brushbsp: remove this
         if (surf_contents.extended & CFLAGS_DETAIL) {
             if (!(surf_contents.native & Q2_CONTENTS_SOLID)) {
                 surf_contents.extended &= ~CFLAGS_DETAIL;
diff --git a/include/common/bspfile.hh b/include/common/bspfile.hh
index 281cb3df..b9c428dc 100644
--- a/include/common/bspfile.hh
+++ b/include/common/bspfile.hh
@@ -626,7 +626,9 @@ struct contentflags_t
 
     constexpr bool clips_same_type() const { return !(extended & CFLAGS_NO_CLIPPING_SAME_TYPE); }
 
-    constexpr bool is_fence() const { return (extended & (CFLAGS_DETAIL_FENCE | CFLAGS_DETAIL_ILLUSIONARY)) != 0; }
+    bool is_fence(const gamedef_t *game) const {
+        return is_detail_fence(game) || is_detail_illusionary(game);
+    }
 
     // check if this content's `type` - which is distinct from various
     // flags that turn things on/off - match. Exactly what the native
@@ -1796,6 +1798,9 @@ struct gamedef_t
     virtual contentflags_t create_solid_contents(const int32_t &cflags = 0) const = 0;
     virtual contentflags_t create_sky_contents(const int32_t &cflags = 0) const = 0;
     virtual contentflags_t create_liquid_contents(const int32_t &liquid_type, const int32_t &cflags = 0) const = 0;
+    virtual contentflags_t create_detail_illusionary_contents(const contentflags_t &original) const = 0;
+    virtual contentflags_t create_detail_fence_contents(const contentflags_t &original) const = 0;
+    virtual contentflags_t create_detail_solid_contents(const contentflags_t &original) const = 0;
     virtual bool contents_are_any_detail(const contentflags_t &contents) const = 0;
     virtual bool contents_are_detail_solid(const contentflags_t &contents) const = 0;
     virtual bool contents_are_detail_fence(const contentflags_t &contents) const = 0;
diff --git a/qbsp/brush.cc b/qbsp/brush.cc
index 404e661d..7b0e05e1 100644
--- a/qbsp/brush.cc
+++ b/qbsp/brush.cc
@@ -896,11 +896,11 @@ static void Brush_LoadEntity(mapentity_t *dst, const mapentity_t *src, const int
         /* turn solid brushes into detail, if we're in hull0 */
         if (hullnum <= 0 && contents.is_solid(options.target_game)) {
             if (detail_illusionary) {
-                contents = {contents.native, CFLAGS_DETAIL_ILLUSIONARY};
+                contents = options.target_game->create_detail_illusionary_contents(contents);
             } else if (detail_fence) {
-                contents = {contents.native, CFLAGS_DETAIL_FENCE};
+                contents = options.target_game->create_detail_fence_contents(contents);
             } else if (detail) {
-                contents = {contents.native, CFLAGS_DETAIL};
+                contents = options.target_game->create_detail_solid_contents(contents);
             }
         }
 
@@ -950,7 +950,7 @@ static void Brush_LoadEntity(mapentity_t *dst, const mapentity_t *src, const int
                 contents type.
                 */
             if (hullnum <= 0 && mirrorinside) {
-                contents = {contents.native, CFLAGS_DETAIL_FENCE};
+                contents = options.target_game->create_detail_fence_contents(contents);
             }
         }
 
diff --git a/qbsp/csg4.cc b/qbsp/csg4.cc
index 6154d34b..adae786e 100644
--- a/qbsp/csg4.cc
+++ b/qbsp/csg4.cc
@@ -300,7 +300,7 @@ static bool ShouldClipbrushEatBrush(const brush_t &brush, const brush_t &clipbru
         || (brush.contents.is_liquid(options.target_game) &&
             clipbrush.contents.is_detail_illusionary(options.target_game))
 
-        || (brush.contents.is_fence() && clipbrush.contents.is_liquid(options.target_game))) {
+        || (brush.contents.is_fence(options.target_game) && clipbrush.contents.is_liquid(options.target_game))) {
         return false;
     }
 
diff --git a/qbsp/writebsp.cc b/qbsp/writebsp.cc
index b777ed12..2690373c 100644
--- a/qbsp/writebsp.cc
+++ b/qbsp/writebsp.cc
@@ -36,13 +36,14 @@ static contentflags_t RemapContentsForExport(const contentflags_t &content)
 {
     if (content.is_detail_fence(options.target_game)) {
         /*
-         * A bit of a hack for Q2, to ensure that structural faces which are completely covered by CFLAGS_DETAIL_FENCE
+         * A bit of a hack for Q2, to ensure that structural faces which are completely covered by detail fence
          * still render.
          *
          * If we export the detail fence leaf as CONTENTS_SOLID, Q2 engines will refuse to render the covered sturctural
          * face because of a short-circuit in GL_DrawLeaf.
          */
         if (options.target_game->id == GAME_QUAKE_II) {
+            // fixme-brushbsp: can remove this once we use WINDOW natively for detail_fence
             return {Q2_CONTENTS_WINDOW, 0};
         }
         /*