diff --git a/src/common/memory_arena.cpp b/src/common/memory_arena.cpp
index 0f44d17ce..74e15092a 100644
--- a/src/common/memory_arena.cpp
+++ b/src/common/memory_arena.cpp
@@ -103,14 +103,37 @@ bool MemoryArena::IsValid() const
 #endif
 }
 
+static std::string GetFileMappingName()
+{
+#if defined(_WIN32)
+  const unsigned pid = GetCurrentThreadId();
+#elif defined(__ANDROID__) || defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
+  const unsigned pid = static_cast<unsigned>(getpid());
+#else
+#error Unknown platform.
+#endif
+
+#ifdef LIBRETRO
+  // libretro second-instance runahead is insane, and loads a second copy of the module in the same process, which means
+  // we'd overlap the memory mapping for the "primary" core. Work around this by taking the address of this function,
+  // which should be unique per instance.
+  std::string ret(StringUtil::StdStringFromFormat("duckstation_%u_%p", pid, ((void*)&GetFileMappingName)));
+#else
+  std::string ret(StringUtil::StdStringFromFormat("duckstation_%u", pid));
+#endif
+
+  Log_InfoPrintf("File mapping name: %s", ret.c_str());
+  return ret;
+}
+
 bool MemoryArena::Create(size_t size, bool writable, bool executable)
 {
   if (IsValid())
     Destroy();
 
-#if defined(WIN32)
-  const std::string file_mapping_name = StringUtil::StdStringFromFormat("duckstation_%u", GetCurrentProcessId());
+  const std::string file_mapping_name(GetFileMappingName());
 
+#if defined(_WIN32)
   const DWORD protect = (writable ? (executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE) : PAGE_READONLY);
   m_file_handle = CreateFileMappingA(INVALID_HANDLE_VALUE, nullptr, protect, Truncate32(size >> 32), Truncate32(size),
                                      file_mapping_name.c_str());
@@ -121,9 +144,7 @@ bool MemoryArena::Create(size_t size, bool writable, bool executable)
   }
 
   return true;
-#elif defined(ANDROID)
-  const std::string file_mapping_name =
-    StringUtil::StdStringFromFormat("duckstation_%u", static_cast<unsigned>(getpid()));
+#elif defined(__ANDROID__)
   m_shmem_fd = AshmemCreateFileMapping(file_mapping_name.c_str(), size);
   if (m_shmem_fd < 0)
   {
@@ -133,8 +154,6 @@ bool MemoryArena::Create(size_t size, bool writable, bool executable)
 
   return true;
 #elif defined(__linux__)
-  const std::string file_mapping_name =
-    StringUtil::StdStringFromFormat("duckstation_%u", static_cast<unsigned>(getpid()));
   m_shmem_fd = shm_open(file_mapping_name.c_str(), O_CREAT | O_EXCL | (writable ? O_RDWR : O_RDONLY), 0600);
   if (m_shmem_fd < 0)
   {
@@ -155,8 +174,6 @@ bool MemoryArena::Create(size_t size, bool writable, bool executable)
   return true;
 #elif defined(__APPLE__) || defined(__FreeBSD__)
 #if defined(__APPLE__)
-  const std::string file_mapping_name =
-    StringUtil::StdStringFromFormat("duckstation_%u", static_cast<unsigned>(getpid()));
   m_shmem_fd = shm_open(file_mapping_name.c_str(), O_CREAT | O_EXCL | (writable ? O_RDWR : O_RDONLY), 0600);
 #else
   m_shmem_fd = shm_open(SHM_ANON, O_CREAT | O_EXCL | (writable ? O_RDWR : O_RDONLY), 0600);