diff --git a/common/bspfile.cc b/common/bspfile.cc
index 4fb302b1..26fd6af4 100644
--- a/common/bspfile.cc
+++ b/common/bspfile.cc
@@ -466,14 +466,15 @@ public:
         if (contents_are_detail_fence(contents) || contents_are_detail_wall(contents)) {
             return create_solid_contents();
         }
+
         if (contents.flags & EWT_VISCONTENTS_MIST) {
             // clear mist. detail_illusionary on its own becomes CONTENTS_EMPTY,
             // detail_illusionary in water becomes CONTENTS_WATER, etc.
-            return contentflags_t::make(contents.flags & ~EWT_VISCONTENTS_MIST);
+            contents = contentflags_t::make(contents.flags & ~EWT_VISCONTENTS_MIST);
         }
         if (contents.flags & EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER) {
             // this exports as empty
-            return contentflags_t::make(contents.flags & ~EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER);
+            contents = contentflags_t::make(contents.flags & ~EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER);
         }
 
         return contents;
@@ -484,14 +485,20 @@ public:
         auto bits_a = a.flags;
         auto bits_b = b.flags;
 
+        auto result = contentflags_t::make(bits_a | bits_b);
+
         if (contents_are_solid(a) || contents_are_solid(b)) {
             return create_solid_contents();
         }
         if (contents_are_sky(a) || contents_are_sky(b)) {
             return contentflags_t::make(EWT_VISCONTENTS_SKY);
         }
+        if ((a.flags & EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER) || (b.flags & EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER)) {
+            // strip out detail flag, otherwise it breaks the visblocker feature
+            result = contentflags_t::make(result.flags & ~EWT_CFLAG_DETAIL);
+        }
 
-        return contentflags_t::make(bits_a | bits_b);
+        return result;
     }
 
     contentflags_t portal_visible_contents(contentflags_t a, contentflags_t b) const override
@@ -1297,6 +1304,11 @@ struct gamedef_q2_t : public gamedef_t
             bits_a &= ~EWT_CFLAG_DETAIL;
             bits_b &= ~EWT_CFLAG_DETAIL;
         }
+        if ((bits_a & EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER) || (bits_b & EWT_VISCONTENTS_ILLUSIONARY_VISBLOCKER)) {
+            // strip out detail flag, otherwise it breaks the visblocker feature
+            bits_a &= ~EWT_CFLAG_DETAIL;
+            bits_b &= ~EWT_CFLAG_DETAIL;
+        }
 
         return contentflags_t::make(bits_a | bits_b);
     }
diff --git a/testmaps/q1_func_illusionary_visblocker_interactions.map b/testmaps/q1_func_illusionary_visblocker_interactions.map
index ff22a6c4..1898264f 100644
--- a/testmaps/q1_func_illusionary_visblocker_interactions.map
+++ b/testmaps/q1_func_illusionary_visblocker_interactions.map
@@ -199,3 +199,35 @@
 "classname" "ambient_flouro_buzz"
 "origin" "280 -48 104"
 }
+// entity 15
+{
+"classname" "func_detail_illusionary"
+"_mirrorinside" "1"
+// brush 0
+{
+( 8 328 -32 ) ( 8 329 -32 ) ( 8 328 -31 ) bolt14 8 -48 0 1 1
+( -56 208 -32 ) ( -56 208 -31 ) ( -55 208 -32 ) bolt14 -8 -48 0 1 1
+( -56 328 16 ) ( -55 328 16 ) ( -56 329 16 ) bolt14 -8 -8 0 1 1
+( 184 376 128 ) ( 184 377 128 ) ( 185 376 128 ) bolt14 -8 -8 0 1 1
+( 184 288 -16 ) ( 185 288 -16 ) ( 184 288 -15 ) bolt14 -8 -48 0 1 1
+( 104 376 -16 ) ( 104 376 -15 ) ( 104 377 -16 ) bolt14 8 -48 0 1 1
+}
+}
+// entity 16
+{
+"classname" "func_illusionary_visblocker"
+// brush 0
+{
+( 16 344 -32 ) ( 16 345 -32 ) ( 16 344 -31 ) *zwater1 56 -48 0 1 1
+( -48 216 -32 ) ( -48 216 -31 ) ( -47 216 -32 ) *zwater1 -16 -48 0 1 1
+( -48 344 16 ) ( -47 344 16 ) ( -48 345 16 ) *zwater1 -16 -56 0 1 1
+( 192 392 120 ) ( 192 393 120 ) ( 193 392 120 ) *zwater1 -16 -56 0 1 1
+( 192 280 -16 ) ( 193 280 -16 ) ( 192 280 -15 ) *zwater1 -16 -48 0 1 1
+( 96 392 -16 ) ( 96 392 -15 ) ( 96 393 -16 ) *zwater1 56 -48 0 1 1
+}
+}
+// entity 17
+{
+"classname" "info_null"
+"origin" "48 248 56"
+}
diff --git a/tests/test_vis.cc b/tests/test_vis.cc
index 51a8c901..91bc2ea2 100644
--- a/tests/test_vis.cc
+++ b/tests/test_vis.cc
@@ -143,6 +143,22 @@ TEST(vis, q1FuncIllusionaryVisblocker)
     }
 }
 
+TEST(vis, q1FuncIllusionaryVisblockerInteractions)
+{
+    SCOPED_TRACE("make sure illusionary_visblocker covered by detail_illusionary doesn't break the visblocker");
+    auto [bsp, bspx, lit] = QbspVisLight_Q1("q1_func_illusionary_visblocker_interactions.map", {}, runvis_t::yes);
+
+    const auto vis = DecompressAllVis(&bsp);
+
+    const auto player_start = qvec3d(80, -272, 40);
+    const auto in_visblocker_covered_by_illusionary = qvec3d(48, 248, 56);
+
+    auto *player_start_leaf = BSP_FindLeafAtPoint(&bsp, &bsp.dmodels[0], player_start);
+    auto *in_visblocker_covered_by_illusionary_leaf = BSP_FindLeafAtPoint(&bsp, &bsp.dmodels[0], in_visblocker_covered_by_illusionary);
+
+    EXPECT_FALSE(q1_leaf_sees(bsp, vis, in_visblocker_covered_by_illusionary_leaf, player_start_leaf));
+}
+
 TEST(vis, ClipStackWinding)
 {
     pstack_t stack{};