diff --git a/light/entities.cc b/light/entities.cc
index a6291685..e3aceaf9 100644
--- a/light/entities.cc
+++ b/light/entities.cc
@@ -320,6 +320,13 @@ static void CheckEntityFields(const mbsp_t *bsp, const settings::worldspawn_keys
         entity->falloff.set_value(0.0f, settings::source::MAP);
     }
 
+    if (entity->getFormula() < 0 || entity->getFormula() >= LF_COUNT) {
+        logging::print("WARNING: unknown delay {} on {} at [{}]\n",
+                       static_cast<int>(entity->getFormula()), entity->classname(), entity->origin.value());
+        entity->formula.set_value(LF_LINEAR, settings::source::MAP);
+        entity->light.set_value(0.0f, settings::source::MAP);
+    }
+
     /* set up deviance and samples defaults */
     if (entity->deviance.value() > 0 && entity->samples.value() == 0) {
         entity->samples.set_value(16, settings::source::MAP);
diff --git a/testmaps/q1_light_invalid_delay.map b/testmaps/q1_light_invalid_delay.map
new file mode 100644
index 00000000..94937fdc
--- /dev/null
+++ b/testmaps/q1_light_invalid_delay.map
@@ -0,0 +1,75 @@
+// Game: Quake
+// Format: Standard
+// entity 0
+{
+"classname" "worldspawn"
+"_tb_textures" "textures/e1u1"
+"_bounce" "0"
+"wad" "deprecated/free_wad.wad"
+// brush 0
+{
+( 480 1088 928 ) ( 480 1089 928 ) ( 480 1088 929 ) bolt14 0 32 0 1 1
+( 704 1088 928 ) ( 704 1088 929 ) ( 705 1088 928 ) bolt14 0 32 0 1 1
+( 704 1088 928 ) ( 705 1088 928 ) ( 704 1089 928 ) bolt14 0 0 0 1 1
+( 944 1472 944 ) ( 944 1473 944 ) ( 945 1472 944 ) bolt14 0 0 0 1 1
+( 944 1488 944 ) ( 945 1488 944 ) ( 944 1488 945 ) bolt14 0 32 0 1 1
+( 1056 1472 944 ) ( 1056 1472 945 ) ( 1056 1473 944 ) bolt14 0 32 0 1 1
+}
+// brush 1
+{
+( 480 1088 1232 ) ( 480 1089 1232 ) ( 480 1088 1233 ) bolt14 0 16 0 1 1
+( 704 1072 1232 ) ( 704 1072 1233 ) ( 705 1072 1232 ) bolt14 0 16 0 1 1
+( 704 1088 1232 ) ( 705 1088 1232 ) ( 704 1089 1232 ) bolt14 0 0 0 1 1
+( 944 1472 1248 ) ( 944 1473 1248 ) ( 945 1472 1248 ) bolt14 0 0 0 1 1
+( 944 1488 1248 ) ( 945 1488 1248 ) ( 944 1488 1249 ) bolt14 0 16 0 1 1
+( 1056 1472 1248 ) ( 1056 1472 1249 ) ( 1056 1473 1248 ) bolt14 0 16 0 1 1
+}
+// brush 2
+{
+( 480 1072 928 ) ( 480 1073 928 ) ( 480 1072 929 ) bolt14 16 32 0 1 1
+( 704 1072 928 ) ( 704 1072 929 ) ( 705 1072 928 ) bolt14 0 32 0 1 1
+( 704 1072 928 ) ( 705 1072 928 ) ( 704 1073 928 ) bolt14 0 -16 0 1 1
+( 944 1456 1248 ) ( 944 1457 1248 ) ( 945 1456 1248 ) bolt14 0 -16 0 1 1
+( 944 1088 944 ) ( 945 1088 944 ) ( 944 1088 945 ) bolt14 0 32 0 1 1
+( 1056 1456 944 ) ( 1056 1456 945 ) ( 1056 1457 944 ) bolt14 16 32 0 1 1
+}
+// brush 3
+{
+( 480 1392 928 ) ( 480 1393 928 ) ( 480 1392 929 ) bolt14 -48 32 0 1 1
+( 832 1488 928 ) ( 832 1488 929 ) ( 833 1488 928 ) bolt14 -128 32 0 1 1
+( 832 1392 928 ) ( 833 1392 928 ) ( 832 1393 928 ) bolt14 -128 48 0 1 1
+( 1072 1776 1248 ) ( 1072 1777 1248 ) ( 1073 1776 1248 ) bolt14 -128 48 0 1 1
+( 1072 1504 944 ) ( 1073 1504 944 ) ( 1072 1504 945 ) bolt14 -128 32 0 1 1
+( 1056 1392 928 ) ( 1056 1392 929 ) ( 1056 1393 928 ) bolt14 -48 32 0 1 1
+}
+// brush 4
+{
+( 1056 1088 1056 ) ( 1056 1089 1056 ) ( 1056 1088 1057 ) bolt14 0 32 0 1 1
+( 736 1088 1056 ) ( 736 1088 1057 ) ( 737 1088 1056 ) bolt14 -32 32 0 1 1
+( 736 1088 928 ) ( 737 1088 928 ) ( 736 1089 928 ) bolt14 -32 0 0 1 1
+( 976 1472 1248 ) ( 976 1473 1248 ) ( 977 1472 1248 ) bolt14 -32 0 0 1 1
+( 976 1488 1072 ) ( 977 1488 1072 ) ( 976 1488 1073 ) bolt14 -32 32 0 1 1
+( 1072 1472 1072 ) ( 1072 1472 1073 ) ( 1072 1473 1072 ) bolt14 0 32 0 1 1
+}
+// brush 5
+{
+( 464 1088 1056 ) ( 464 1089 1056 ) ( 464 1088 1057 ) bolt14 0 32 0 1 1
+( 144 1072 1056 ) ( 144 1072 1057 ) ( 145 1072 1056 ) bolt14 48 32 0 1 1
+( 144 1088 928 ) ( 145 1088 928 ) ( 144 1089 928 ) bolt14 48 0 0 1 1
+( 384 1472 1248 ) ( 384 1473 1248 ) ( 385 1472 1248 ) bolt14 48 0 0 1 1
+( 384 1488 1072 ) ( 385 1488 1072 ) ( 384 1488 1073 ) bolt14 48 32 0 1 1
+( 480 1472 1072 ) ( 480 1472 1073 ) ( 480 1473 1072 ) bolt14 0 32 0 1 1
+}
+}
+// entity 1
+{
+"classname" "info_player_start"
+"origin" "976 1408 968"
+"angle" "180"
+}
+// entity 2
+{
+"classname" "light"
+"origin" "568 1288 1080"
+"delay" "15"
+}
diff --git a/tests/test_ltface.cc b/tests/test_ltface.cc
index 24a78970..4bac7920 100644
--- a/tests/test_ltface.cc
+++ b/tests/test_ltface.cc
@@ -949,6 +949,17 @@ TEST_CASE("q1_light_sun_artifact")
     }
 }
 
+TEST_CASE("q1_light_invalid_delay")
+{
+    INFO("invalid light formulas are ignored, not a fatal error");
+
+    auto [bsp, bspx, lit] = QbspVisLight_Q1("q1_light_invalid_delay.map", {"-lit"});
+
+    for (const auto &face : bsp.dfaces) {
+        CheckFaceLuxels(bsp, face, [](qvec3b sample) { CHECK(sample == qvec3b(0, 0, 0)); }, &lit);
+    }
+}
+
 TEST_CASE("q1_light_bounce_litwater without the water")
 {
     auto [bsp, bspx] = QbspVisLight_Common("q1_light_bounce_litwater.map", {"-omitdetail"}, {"-lit", "-bounce", "4"}, runvis_t::no);