diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index ad73c74f33..9138486a7d 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -30,6 +30,7 @@
 - Fix: [#15476] Crash when placing/clearing small scenery.
 - Fix: [#15487] Map animations do not work correctly when loading an exported SV6 file in vanilla RCT2.
 - Fix: [#15496] Crash in paint_swinging_inverter_ship_structure().
+- Fix: [#15503] Freeze when doing specific coaster merges with block brakes.
 - Fix: [#15514] Two different “quit to menu” menu items are available in track designer and track design manager.
 - Improved: [#3417] Crash dumps are now placed in their own folder.
 - Change: [#8601] Revert ToonTower base block fix to re-enable support blocking.
diff --git a/src/openrct2/ride/Ride.cpp b/src/openrct2/ride/Ride.cpp
index d90387ee35..1eabd0f6cf 100644
--- a/src/openrct2/ride/Ride.cpp
+++ b/src/openrct2/ride/Ride.cpp
@@ -3492,8 +3492,16 @@ void Ride::MoveTrainsToBlockBrakes(TrackElement* firstBlock)
             continue;
         }
 
+        size_t numIterations = 0;
         do
         {
+            // Fixes both freezing issues in #15503.
+            // TODO: refactor the code so a tortoise-and-hare algorithm can be used.
+            if (numIterations++ > 1000000)
+            {
+                break;
+            }
+
             firstBlock->SetBlockBrakeClosed(true);
             for (Vehicle* car = train; car != nullptr; car = GetEntity<Vehicle>(car->next_vehicle_on_train))
             {