diff --git a/common/bspfile.cc b/common/bspfile.cc
index 1e6a76ed..fcb3beb2 100644
--- a/common/bspfile.cc
+++ b/common/bspfile.cc
@@ -80,6 +80,8 @@ struct gamedef_generic_t : public gamedef_t
 
     bool portal_can_see_through(const contentflags_t &, const contentflags_t &) const { throw std::bad_cast(); }
 
+    bool contents_seals_map(const contentflags_t &contents) const { throw std::bad_cast(); }
+
     std::string get_contents_display(const contentflags_t &) const { throw std::bad_cast(); }
 
     const std::initializer_list<aabb3d> &get_hull_sizes() const { throw std::bad_cast(); }
@@ -252,6 +254,11 @@ struct gamedef_q1_like_t : public gamedef_t
         return !(contents0.is_solid(this) || contents1.is_solid(this)) && contents0 == contents1;
     }
 
+    bool contents_seals_map(const contentflags_t &contents) const override
+    {
+        return contents_are_solid(contents) || contents_are_sky(contents);
+    }
+
     std::string get_contents_display(const contentflags_t &contents) const
     {
         switch (contents.native) {
@@ -587,6 +594,11 @@ struct gamedef_q2_t : public gamedef_t
         return visible_contents(c0 ^ c1);
     }
 
+    bool contents_seals_map(const contentflags_t& contents) const override
+    {
+        return contents_are_solid(contents) || contents_are_sky(contents);
+    }
+
     std::string get_contents_display(const contentflags_t &contents) const
     {
         constexpr const char *bitflag_names[] = {"SOLID", "WINDOW", "AUX", "LAVA", "SLIME", "WATER", "MIST", "128",
diff --git a/include/common/bspfile.hh b/include/common/bspfile.hh
index dbd8c4de..ef95d04f 100644
--- a/include/common/bspfile.hh
+++ b/include/common/bspfile.hh
@@ -1781,6 +1781,7 @@ struct gamedef_t
     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 contents_seals_map(const contentflags_t &contents) const = 0;
     virtual std::string get_contents_display(const contentflags_t &contents) const = 0;
     virtual const std::initializer_list<aabb3d> &get_hull_sizes() const = 0;
     virtual contentflags_t face_get_contents(