diff --git a/common/bspfile.cc b/common/bspfile.cc
index 36071be5..72ce3212 100644
--- a/common/bspfile.cc
+++ b/common/bspfile.cc
@@ -98,7 +98,7 @@ struct gamedef_generic_t : public gamedef_t
 
     bool contents_are_valid(const contentflags_t &, bool) const override { throw std::bad_cast(); }
 
-    bool portal_can_see_through(const contentflags_t &, const contentflags_t &) const override { throw std::bad_cast(); }
+    bool portal_can_see_through(const contentflags_t &, const contentflags_t &, bool, bool) const override { throw std::bad_cast(); }
 
     bool contents_seals_map(const contentflags_t &contents) const override { throw std::bad_cast(); }
 
@@ -385,8 +385,24 @@ public:
         }
     }
 
-    bool portal_can_see_through(const contentflags_t &contents0, const contentflags_t &contents1) const
+    bool portal_can_see_through(const contentflags_t &contents0, const contentflags_t &contents1, bool transwater, bool transsky) const
     {
+        /* If water is transparent, liquids are like empty space */
+        if (transwater) {
+            if (contents_are_liquid(contents0) && contents_are_empty(contents1))
+                return true;
+            if (contents_are_liquid(contents1) && contents_are_empty(contents0))
+                return true;
+        }
+
+        /* If sky is transparent, then sky is like empty space */
+        if (transsky) {
+            if (contents_are_sky(contents0) && contents_are_empty(contents1))
+                return true;
+            if (contents_are_empty(contents0) && contents_are_sky(contents1))
+                return true;
+        }
+
         /* If contents values are the same and not solid, can see through */
         return !(contents0.is_solid(this) || contents1.is_solid(this)) && contents0.equals(this, contents1);
     }
@@ -918,7 +934,7 @@ struct gamedef_q2_t : public gamedef_t
         return 0;
     }
 
-    bool portal_can_see_through(const contentflags_t &contents0, const contentflags_t &contents1) const
+    bool portal_can_see_through(const contentflags_t &contents0, const contentflags_t &contents1, bool, bool) const
     {
         int32_t c0 = contents0.native, c1 = contents1.native;
 
diff --git a/include/common/bspfile.hh b/include/common/bspfile.hh
index 99084b7a..287e8fba 100644
--- a/include/common/bspfile.hh
+++ b/include/common/bspfile.hh
@@ -1810,7 +1810,7 @@ struct gamedef_t
     virtual bool contents_are_sky(const contentflags_t &contents) const = 0;
     virtual bool contents_are_liquid(const contentflags_t &contents) const = 0;
     virtual bool contents_are_valid(const contentflags_t &contents, bool strict = true) const = 0;
-    virtual bool portal_can_see_through(const contentflags_t &contents0, const contentflags_t &contents1) const = 0;
+    virtual bool portal_can_see_through(const contentflags_t &contents0, const contentflags_t &contents1, bool transwater, bool transsky) const = 0;
     virtual bool contents_seals_map(const contentflags_t &contents) const = 0;
     virtual contentflags_t contents_remap_for_export(const contentflags_t &contents) const = 0;
     virtual contentflags_t combine_contents(const contentflags_t &a, const contentflags_t &b) const = 0;
diff --git a/qbsp/portals.cc b/qbsp/portals.cc
index 245af472..9d7fb495 100644
--- a/qbsp/portals.cc
+++ b/qbsp/portals.cc
@@ -77,28 +77,8 @@ static bool PortalThru(const portal_t *p)
     if (contents0.illusionary_visblocker || contents1.illusionary_visblocker)
         return false;
 
-    // FIXME: we can't move this directly to portal_can_see_through because
-    // "options" isn't exposed there.
-    if (options.target_game->id != GAME_QUAKE_II) {
-        /* If water is transparent, liquids are like empty space */
-        if (options.transwater.value()) {
-            if (contents0.is_liquid(options.target_game) && contents1.is_empty(options.target_game))
-                return true;
-            if (contents1.is_liquid(options.target_game) && contents0.is_empty(options.target_game))
-                return true;
-        }
-
-        /* If sky is transparent, then sky is like empty space */
-        if (options.transsky.value()) {
-            if (contents0.is_sky(options.target_game) && contents1.is_empty(options.target_game))
-                return true;
-            if (contents0.is_empty(options.target_game) && contents1.is_sky(options.target_game))
-                return true;
-        }
-    }
-
     // Check per-game visibility
-    return options.target_game->portal_can_see_through(contents0, contents1);
+    return options.target_game->portal_can_see_through(contents0, contents1, options.transwater.value(), options.transsky.value());
 }
 
 static void WritePortals_r(node_t *node, std::ofstream &portalFile, bool clusters)