diff --git a/Externals/OPCODE/pch.cpp b/Externals/OPCODE/pch.cpp
index 3854579ae1c..e090d88a6af 100644
--- a/Externals/OPCODE/pch.cpp
+++ b/Externals/OPCODE/pch.cpp
@@ -1 +1,7 @@
 #include "pch.hpp"
+
+#ifdef USE_ARENA_ALLOCATOR
+static const u32 s_arena_size = (128 + 16) * 1024 * 1024;
+static char s_fake_array[s_arena_size];
+doug_lea_allocator g_collision_allocator(s_fake_array, s_arena_size, "opcode");
+#endif // #ifdef USE_ARENA_ALLOCATOR