diff --git a/common/bspfile.cc b/common/bspfile.cc
index 215f4199..9662ec5b 100644
--- a/common/bspfile.cc
+++ b/common/bspfile.cc
@@ -1227,7 +1227,8 @@ struct gamedef_q2_t : public gamedef_t
                 // windows don't generate inside faces
                 return false;
             }
-            return true;
+            // other types get mirrored by default, unless we override it with mirror_inside
+            return brushcontents.mirror_inside.value_or(true);
         }
         return true;
     }
diff --git a/testmaps/qbsp_q2_mirrorinside.map b/testmaps/qbsp_q2_mirrorinside.map
new file mode 100644
index 00000000..632abd23
--- /dev/null
+++ b/testmaps/qbsp_q2_mirrorinside.map
@@ -0,0 +1,90 @@
+// Game: Quake 2
+// Format: Quake2 (Valve)
+// entity 0
+{
+"mapversion" "220"
+"classname" "worldspawn"
+"_tb_textures" "textures/e1u1;textures/e1u2;textures/e1u3;textures/e1u4;textures/e2u1;textures/e2u2;textures/e2u3;textures/e3u1;textures/e3u2;textures/e3u3"
+// brush 0
+{
+( -176 -256 64 ) ( -176 -255 64 ) ( -176 -256 65 ) e1u1/ggrat4_2 [ 0 1.0000000000000002 0 -16 ] [ 0 0 -1.0000000000000002 -32 ] 0 1 1
+( -176 -432 64 ) ( -176 -432 65 ) ( -175 -432 64 ) e1u1/ggrat4_2 [ -1 0 0 -16 ] [ 0 0 -1 -32 ] 0 1 1
+( -176 -256 96 ) ( -175 -256 96 ) ( -176 -255 96 ) e1u1/ggrat4_2 [ -1.0000000000000002 0 0 -16 ] [ 0 1.0000000000000002 0 -48 ] 0 1 1
+( -160 192 352 ) ( -160 193 352 ) ( -159 192 352 ) e1u1/ggrat4_2 [ -1.0000000000000002 0 0 -16 ] [ 0 -1.0000000000000002 0 -80 ] 0 1 1
+( -160 176 80 ) ( -159 176 80 ) ( -160 176 81 ) e1u1/ggrat4_2 [ -1 0 0 -16 ] [ 0 0 -1 -32 ] 0 1 1
+( -160 192 80 ) ( -160 192 81 ) ( -160 193 80 ) e1u1/ggrat4_2 [ 0 -1.0000000000000002 0 64 ] [ 0 0 -1.0000000000000002 -32 ] 0 1 1
+}
+// brush 1
+{
+( -160 176 88 ) ( -160 177 88 ) ( -160 176 89 ) e1u1/ggrat4_2 [ 0 1.0000000000000002 0 -32 ] [ 0 0 -1.0000000000000002 -32 ] 0 1 1
+( -160 176 88 ) ( -160 176 89 ) ( -159 176 88 ) e1u1/ggrat4_2 [ -1 0 0 -16 ] [ 0 0 -1 -32 ] 0 1 1
+( -160 176 96 ) ( -159 176 96 ) ( -160 177 96 ) e1u1/ggrat4_2 [ -1.0000000000000002 0 0 -16 ] [ 0 1.0000000000000002 0 -40 ] 0 1 1
+( 288 192 352 ) ( 288 193 352 ) ( 289 192 352 ) e1u1/ggrat4_2 [ -1.0000000000000002 0 0 -16 ] [ 0 -1.0000000000000002 0 48 ] 0 1 1
+( 288 192 96 ) ( 289 192 96 ) ( 288 192 97 ) e1u1/ggrat4_2 [ -1 0 0 -16 ] [ 0 0 -1 -32 ] 0 1 1
+( 288 192 96 ) ( 288 192 97 ) ( 288 193 96 ) e1u1/ggrat4_2 [ 0 -1.0000000000000002 0 0 ] [ 0 0 -1.0000000000000002 -32 ] 0 1 1
+}
+// brush 2
+{
+( -160 -112 96 ) ( -160 -111 96 ) ( -160 -112 97 ) e1u1/florr1_8 [ 0 1 0 -16 ] [ 0 0 -1 0 ] 0 1 1
+( -80 -432 80 ) ( -81 -432 80 ) ( -80 -432 81 ) e1u1/florr1_8 [ -1 0 0 16 ] [ 0 0 -1 0 ] 180 1 1
+( -80 -432 80 ) ( -80 -431 80 ) ( -81 -432 80 ) e1u1/florr1_8 [ 1 0 0 -16 ] [ 0 -1 0 16 ] 180 1 1
+( -160 -112 96 ) ( -161 -112 96 ) ( -160 -111 96 ) e1u1/florr1_8 [ -1 0 0 16 ] [ 0 -1 0 16 ] 180 1 1
+( -160 176 96 ) ( -160 176 97 ) ( -161 176 96 ) e1u1/florr1_8 [ 1 0 0 -16 ] [ 0 0 -1 0 ] 180 1 1
+( 288 -432 80 ) ( 288 -432 81 ) ( 288 -431 80 ) e1u1/florr1_8 [ 0 -1 0 16 ] [ 0 0 -1 0 ] 0 1 1
+}
+// brush 3
+{
+( -160 -448 88 ) ( -160 -447 88 ) ( -160 -448 89 ) e1u1/ggrat4_2 [ 0 1 0 0 ] [ 0 0 -1 -32 ] 0 1 1
+( -160 -448 88 ) ( -160 -448 89 ) ( -159 -448 88 ) e1u1/ggrat4_2 [ -1.0000000000000002 0 0 -32 ] [ 0 0 -1.0000000000000002 -32 ] 0 1 1
+( -160 -448 96 ) ( -159 -448 96 ) ( -160 -447 96 ) e1u1/ggrat4_2 [ 0 1.0000000000000002 0 0 ] [ 1.0000000000000002 0 0 -32 ] 0 1 1
+( 288 -432 352 ) ( 288 -431 352 ) ( 289 -432 352 ) e1u1/ggrat4_2 [ 0 1.0000000000000002 0 0 ] [ -1.0000000000000002 0 0 -96 ] 0 1 1
+( 288 -432 96 ) ( 289 -432 96 ) ( 288 -432 97 ) e1u1/ggrat4_2 [ 1.0000000000000002 0 0 -80 ] [ 0 0 -1.0000000000000002 -32 ] 0 1 1
+( 288 -432 96 ) ( 288 -432 97 ) ( 288 -431 96 ) e1u1/ggrat4_2 [ 0 1 0 0 ] [ 0 0 -1 -32 ] 0 1 1
+}
+// brush 4
+{
+( -160 -256 352 ) ( -160 -255 352 ) ( -160 -256 353 ) e1u1/florr1_8 [ 0 0 -1.0000000000000002 0 ] [ 0 -1.0000000000000002 0 0 ] 180 1 1
+( 288 -432 360 ) ( 288 -432 361 ) ( 289 -432 360 ) e1u1/florr1_8 [ -1.0000000000000002 0 0 0 ] [ 0 0 1.0000000000000002 -16 ] 180 1 1
+( -160 -256 352 ) ( -159 -256 352 ) ( -160 -255 352 ) e1u1/florr1_8 [ -1 0 0 0 ] [ 0 -1 0 0 ] 180 1 1
+( 288 176 368 ) ( 288 177 368 ) ( 289 176 368 ) e1u1/florr1_8 [ -1 0 0 0 ] [ 0 -1 0 0 ] 180 1 1
+( 288 176 360 ) ( 289 176 360 ) ( 288 176 361 ) e1u1/florr1_8 [ -1.0000000000000002 0 0 0 ] [ 0 0 1.0000000000000002 -16 ] 180 1 1
+( 288 176 360 ) ( 288 176 361 ) ( 288 177 360 ) e1u1/florr1_8 [ 0 0 1.0000000000000002 0 ] [ 0 -1.0000000000000002 0 0 ] 180 1 1
+}
+// brush 5
+{
+( 288 192 80 ) ( 288 193 80 ) ( 288 192 81 ) e1u1/ggrat4_2 [ 0 1 0 0 ] [ 0 0 -1 -32 ] 0 1 1
+( 304 -432 64 ) ( 303 -432 64 ) ( 304 -432 65 ) e1u1/ggrat4_2 [ -1 0 0 16 ] [ 0 0 -1 -32 ] 180 1 1
+( 304 -256 96 ) ( 304 -255 96 ) ( 303 -256 96 ) e1u1/ggrat4_2 [ 1 0 0 -16 ] [ 0 -1 0 0 ] 180 1 1
+( 304 -256 352 ) ( 303 -256 352 ) ( 304 -255 352 ) e1u1/ggrat4_2 [ 1 0 0 -16 ] [ 0 -1 0 0 ] 180 1 1
+( 288 176 80 ) ( 288 176 81 ) ( 287 176 80 ) e1u1/ggrat4_2 [ 1 0 0 -16 ] [ 0 0 -1 -32 ] 180 1 1
+( 304 -256 64 ) ( 304 -256 65 ) ( 304 -255 64 ) e1u1/ggrat4_2 [ 0 -1 0 0 ] [ 0 0 -1 -32 ] 0 1 1
+}
+// brush 6
+{
+( 32 -80 112 ) ( 32 -79 112 ) ( 32 -80 113 ) e1u1/brwater [ 0 -1 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+( 32 -80 112 ) ( 32 -80 113 ) ( 33 -80 112 ) e1u1/brwater [ 1 0 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+( 32 -80 112 ) ( 33 -80 112 ) ( 32 -79 112 ) e1u1/brwater [ -1 0 0 0 ] [ 0 -1 0 0 ] 0 1 1 64 0 100
+( 112 32 192 ) ( 112 33 192 ) ( 113 32 192 ) e1u1/brwater [ 1 0 0 0 ] [ 0 -1 0 0 ] 0 1 1 64 0 100
+( 112 32 128 ) ( 113 32 128 ) ( 112 32 129 ) e1u1/brwater [ -1 0 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+( 112 32 128 ) ( 112 32 129 ) ( 112 33 128 ) e1u1/brwater [ 0 1 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+}
+}
+// entity 1
+{
+"classname" "info_player_start"
+"origin" "-88 -112 120"
+}
+// entity 2
+{
+"classname" "func_group"
+"_mirrorinside" "0"
+// brush 0
+{
+( 32 -272 112 ) ( 32 -271 112 ) ( 32 -272 113 ) e1u1/brwater [ 0 -1 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+( 32 -272 112 ) ( 32 -272 113 ) ( 33 -272 112 ) e1u1/brwater [ 1 0 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+( 32 -272 112 ) ( 33 -272 112 ) ( 32 -271 112 ) e1u1/brwater [ -1 0 0 0 ] [ 0 -1 0 0 ] 0 1 1 64 0 100
+( 112 -160 192 ) ( 112 -159 192 ) ( 113 -160 192 ) e1u1/brwater [ 1 0 0 0 ] [ 0 -1 0 0 ] 0 1 1 64 0 100
+( 112 -160 128 ) ( 113 -160 128 ) ( 112 -160 129 ) e1u1/brwater [ -1 0 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+( 112 -160 128 ) ( 112 -160 129 ) ( 112 -159 128 ) e1u1/brwater [ 0 1 0 0 ] [ 0 0 -1 0 ] 0 1 1 64 0 100
+}
+}
diff --git a/tests/test_qbsp_q2.cc b/tests/test_qbsp_q2.cc
index 938b9da8..1eef1618 100644
--- a/tests/test_qbsp_q2.cc
+++ b/tests/test_qbsp_q2.cc
@@ -501,3 +501,22 @@ TEST_CASE("q2_door" * doctest::test_suite("testmaps_q2")) {
     CHECK(bmodel_tight_bounds.mins() == bsp.dmodels[1].mins);
     CHECK(bmodel_tight_bounds.maxs() == bsp.dmodels[1].maxs);
 }
+
+TEST_CASE("q2_mirrorinside" * doctest::test_suite("testmaps_q2"))
+{
+    const auto [bsp, bspx, prt] = LoadTestmapQ2("qbsp_q2_mirrorinside.map");
+
+    {
+        INFO("mist is two sided by default");
+        const qvec3d mist_pos{32, -28, 156};
+        CHECK_VECTORS_UNOREDERED_EQUAL(TexNames(bsp, BSP_FindFacesAtPoint(&bsp, &bsp.dmodels[0], mist_pos)),
+            std::vector<std::string>({"e1u1/brwater", "e1u1/brwater"}));
+    }
+
+    {
+        INFO("_mirrorinside 0 disables the inside faces on mist");
+        const qvec3d mist_mirrorinside0_pos{32, -224, 156};
+        CHECK_VECTORS_UNOREDERED_EQUAL(TexNames(bsp, BSP_FindFacesAtPoint(&bsp, &bsp.dmodels[0], mist_mirrorinside0_pos)),
+            std::vector<std::string>({"e1u1/brwater"}));
+    }
+}