diff --git a/docs/tr1/CHANGELOG.md b/docs/tr1/CHANGELOG.md
index 14254827f..2993df73c 100644
--- a/docs/tr1/CHANGELOG.md
+++ b/docs/tr1/CHANGELOG.md
@@ -59,6 +59,7 @@
 - fixed the `/play` console command resulting in Lara starting the target level without pistols (#1861, regression from 4.5)
 - fixed the demo mode text overlapping with the enemy health bar if the health bar is located in the bottom centered (#1446)
 - fixed mutant explosions sometimes heavily damaging Lara even if they missed (#1758, regression since 4.5)
+- fixed wrongly calculated trapdoor size that could affect custom levels (#1904)
 - improved enemy item drops by supporting the TR2+ approach of having drops defined in level data (#1713)
 - improved Italian localization for the Config Tool
 - improved the injection approach for Lara's responsive jumping (#1823)
diff --git a/src/tr1/game/objects/general/trapdoor.c b/src/tr1/game/objects/general/trapdoor.c
index efe9616d1..db7202ef5 100644
--- a/src/tr1/game/objects/general/trapdoor.c
+++ b/src/tr1/game/objects/general/trapdoor.c
@@ -3,6 +3,8 @@
 #include "game/items.h"
 #include "global/const.h"
 
+#include <libtrx/utils.h>
+
 typedef enum {
     TRAPDOOR_STATE_CLOSED,
     TRAPDOOR_STATE_OPEN,
@@ -12,20 +14,40 @@ static bool M_IsItemOnTop(const ITEM *item, int32_t x, int32_t z);
 
 static bool M_IsItemOnTop(const ITEM *item, int32_t x, int32_t z)
 {
-    int32_t tx = item->pos.x >> WALL_SHIFT;
-    int32_t tz = item->pos.z >> WALL_SHIFT;
-    x >>= WALL_SHIFT;
-    z >>= WALL_SHIFT;
+    const BOUNDS_16 *const orig_bounds = &Item_GetBestFrame(item)->bounds;
+    BOUNDS_16 fixed_bounds = { 0 };
 
-    if (item->rot.y == 0 && x == tx && (z == tz || z == tz + 1)) {
-        return true;
-    } else if (item->rot.y == -PHD_180 && x == tx && (z == tz || z == tz - 1)) {
-        return true;
-    } else if (item->rot.y == PHD_90 && z == tz && (x == tx || x == tx + 1)) {
-        return true;
-    } else if (item->rot.y == -PHD_90 && z == tz && (x == tx || x == tx - 1)) {
+    // Bounds need to change in order to account for 2 sector trapdoors
+    // and the trapdoor angle.
+    if (item->rot.y == 0) {
+        fixed_bounds.min.x = orig_bounds->min.x;
+        fixed_bounds.max.x = orig_bounds->max.x;
+        fixed_bounds.min.z = orig_bounds->min.z;
+        fixed_bounds.max.z = orig_bounds->max.z;
+    } else if (item->rot.y == PHD_90) {
+        fixed_bounds.min.x = orig_bounds->min.z;
+        fixed_bounds.max.x = orig_bounds->max.z;
+        fixed_bounds.min.z = -orig_bounds->max.x;
+        fixed_bounds.max.z = -orig_bounds->min.x;
+    } else if (item->rot.y == -PHD_180) {
+        fixed_bounds.min.x = -orig_bounds->max.x;
+        fixed_bounds.max.x = -orig_bounds->min.x;
+        fixed_bounds.min.z = -orig_bounds->max.z;
+        fixed_bounds.max.z = -orig_bounds->min.z;
+    } else if (item->rot.y == -PHD_90) {
+        fixed_bounds.min.x = -orig_bounds->max.z;
+        fixed_bounds.max.x = -orig_bounds->min.z;
+        fixed_bounds.min.z = orig_bounds->min.x;
+        fixed_bounds.max.z = orig_bounds->max.x;
+    }
+
+    if (x <= item->pos.x + fixed_bounds.max.x
+        && x >= item->pos.x + fixed_bounds.min.x
+        && z <= item->pos.z + fixed_bounds.max.z
+        && z >= item->pos.z + fixed_bounds.min.z) {
         return true;
     }
+
     return false;
 }