diff --git a/src/map_memory.cpp b/src/map_memory.cpp
index d3179b3653cc5..f09b3e29d2223 100644
--- a/src/map_memory.cpp
+++ b/src/map_memory.cpp
@@ -2,62 +2,80 @@
 
 #include <algorithm>
 
-void map_memory::trim( int limit )
+template<typename T>
+T lru_cache<T>::get( const tripoint &pos, const T &default_ ) const
 {
-    while( tiles.size() > static_cast<size_t>( limit ) ) {
-        tile_map.erase( tiles.back().first );
-        tiles.pop_back();
+    auto found = map.find( pos );
+    if( found != map.end() ) {
+        return found->second->second;
     }
-    while( symbols.size() > static_cast<size_t>( limit ) ) {
-        symbol_map.erase( symbols.back().first );
-        symbols.pop_back();
+    return default_;
+}
+
+template<typename T>
+void lru_cache<T>::insert( int limit, const tripoint &pos, const T &t )
+{
+    auto found = map.find( pos );
+
+    if( found == map.end() ) {
+        // Need new entry in map.  Make the new list entry and point to it.
+        ordered_list.emplace_back( pos, t );
+        map[pos] = std::prev( ordered_list.end() );
+        trim( limit );
+    } else {
+        // Splice existing entry to the back.  Does not invalidate the
+        // iterator, so no need to change the map.
+        auto list_iterator = found->second;
+        ordered_list.splice( ordered_list.end(), ordered_list, list_iterator );
+        // Update the moved item
+        list_iterator->second = t;
     }
 }
 
-memorized_terrain_tile map_memory::get_tile( const tripoint &pos ) const
+template<typename T>
+void lru_cache<T>::trim( int limit )
 {
-    auto found_tile = tile_map.find( pos );
-    if( found_tile != tile_map.end() ) {
-        return found_tile->second->second;
+    while( ordered_list.size() > static_cast<size_t>( limit ) ) {
+        map.erase( ordered_list.front().first );
+        ordered_list.pop_front();
     }
-    return { "", 0, 0 };
+}
+
+template<typename T>
+void lru_cache<T>::clear()
+{
+    map.clear();
+    ordered_list.clear();
+}
+
+template<typename T>
+const std::list<typename lru_cache<T>::Pair> &lru_cache<T>::list() const
+{
+    return ordered_list;
+}
+
+template class lru_cache<memorized_terrain_tile>;
+template class lru_cache<long>;
+
+static const memorized_terrain_tile default_tile{ "", 0, 0 };
+
+memorized_terrain_tile map_memory::get_tile( const tripoint &pos ) const
+{
+    return tile_cache.get( pos, default_tile );
 }
 
 void map_memory::memorize_tile( int limit, const tripoint &pos, const std::string &ter,
                                 const int subtile, const int rotation )
 {
-    memorized_terrain_tile new_tile{ ter, subtile, rotation };
-    tiles.push_front( std::make_pair( pos, new_tile ) );
-    auto found_tile = tile_map.find( pos );
-    if( found_tile != tile_map.end() ) {
-        // Remove redundant entry since we pushed one to the front.
-        tiles.erase( found_tile->second );
-        found_tile->second = tiles.begin();
-    } else {
-        tile_map[pos] = tiles.begin();
-        trim( limit );
-    }
+    tile_cache.insert( limit, pos, memorized_terrain_tile{ ter, subtile, rotation } );
 }
 
 long map_memory::get_symbol( const tripoint &pos ) const
 {
-    auto found_tile = symbol_map.find( pos );
-    if( found_tile != symbol_map.end() ) {
-        return found_tile->second->second;
-    }
-    return 0;
+    return symbol_cache.get( pos, 0 );
 }
 
 void map_memory::memorize_symbol( int limit, const tripoint &pos, const long symbol )
 {
-    symbols.emplace_front( pos, symbol );
-    auto found_tile = symbol_map.find( pos );
-    if( found_tile != symbol_map.end() ) {
-        // Remove redundant entry since we pushed on to the front.
-        symbols.erase( found_tile->second );
-        found_tile->second = symbols.begin();
-    } else {
-        symbol_map[pos] = symbols.begin();
-        trim( limit );
-    }
+    symbol_cache.insert( limit, pos, symbol );
 }
diff --git a/src/map_memory.h b/src/map_memory.h
index 3dac6131cdbd4..beb26644b8d15 100644
--- a/src/map_memory.h
+++ b/src/map_memory.h
@@ -17,6 +17,26 @@ struct memorized_terrain_tile {
     int rotation;
 };
 
+template<typename T>
+class lru_cache
+{
+    public:
+        using Pair = std::pair<tripoint, T>;
+
+        void insert( int limit, const tripoint &, const T & );
+        T get( const tripoint &, const T &default_ ) const;
+
+        void clear();
+        const std::list<Pair> &list() const;
+    private:
+        void trim( int limit );
+        std::list<Pair> ordered_list;
+        std::unordered_map<tripoint, typename std::list<Pair>::iterator> map;
+};
+
+extern template class lru_cache<memorized_terrain_tile>;
+extern template class lru_cache<long>;
+
 class map_memory
 {
     public:
@@ -33,12 +53,8 @@ class map_memory
         long get_symbol( const tripoint &p ) const;
     private:
         void trim( int limit );
-        using tile_pair = std::pair<tripoint, memorized_terrain_tile>;
-        std::list<tile_pair> tiles;
-        std::unordered_map<tripoint, std::list<tile_pair>::iterator> tile_map;
-        using symbol_pair = std::pair<tripoint, long>;
-        std::list<symbol_pair> symbols;
-        std::unordered_map<tripoint, std::list<symbol_pair>::iterator> symbol_map;
+        lru_cache<memorized_terrain_tile> tile_cache;
+        lru_cache<long> symbol_cache;
 };
 
 #endif
diff --git a/src/savegame_json.cpp b/src/savegame_json.cpp
index 5867ad4d524f1..724388bd4af24 100644
--- a/src/savegame_json.cpp
+++ b/src/savegame_json.cpp
@@ -2613,7 +2613,7 @@ void map_memory::store( JsonOut &jsout ) const
 {
     jsout.member( "map_memory_tiles" );
     jsout.start_array();
-    for( const auto &elem : tiles ) {
+    for( const auto &elem : tile_cache.list() ) {
         jsout.start_object();
         jsout.member( "x", elem.first.x );
         jsout.member( "y", elem.first.y );
@@ -2627,7 +2627,7 @@ void map_memory::store( JsonOut &jsout ) const
 
     jsout.member( "map_memory_curses" );
     jsout.start_array();
-    for( const auto &elem : symbols ) {
+    for( const auto &elem : symbol_cache.list() ) {
         jsout.start_object();
         jsout.member( "x", elem.first.x );
         jsout.member( "y", elem.first.y );
@@ -2641,8 +2641,7 @@ void map_memory::store( JsonOut &jsout ) const
 void map_memory::load( JsonObject &jsin )
 {
     JsonArray map_memory_tiles = jsin.get_array( "map_memory_tiles" );
-    tiles.clear();
-    tile_map.clear();
+    tile_cache.clear();
     while( map_memory_tiles.has_more() ) {
         JsonObject pmap = map_memory_tiles.next_object();
         const tripoint p( pmap.get_int( "x" ), pmap.get_int( "y" ), pmap.get_int( "z" ) );
@@ -2651,8 +2650,7 @@ void map_memory::load( JsonObject &jsin )
     }
 
     JsonArray map_memory_curses = jsin.get_array( "map_memory_curses" );
-    symbols.clear();
-    symbol_map.clear();
+    symbol_cache.clear();
     while( map_memory_curses.has_more() ) {
         JsonObject pmap = map_memory_curses.next_object();
         const tripoint p( pmap.get_int( "x" ), pmap.get_int( "y" ), pmap.get_int( "z" ) );
diff --git a/tests/map_memory.cpp b/tests/map_memory.cpp
new file mode 100644
index 0000000000000..77856802c3798
--- /dev/null
+++ b/tests/map_memory.cpp
@@ -0,0 +1,85 @@
+#include "catch/catch.hpp"
+
+#include "map_memory.h"
+#include "json.h"
+
+static const tripoint p1{ 0, 0, 1 };
+static const tripoint p2{ 0, 0, 2 };
+static const tripoint p3{ 0, 0, 3 };
+
+TEST_CASE( "map_memory_defaults", "[map_memory]" )
+{
+    map_memory memory;
+    CHECK( memory.get_symbol( p1 ) == 0 );
+    memorized_terrain_tile default_tile = memory.get_tile( p1 );
+    CHECK( default_tile.tile == "" );
+    CHECK( default_tile.subtile == 0 );
+    CHECK( default_tile.rotation == 0 );
+}
+
+TEST_CASE( "map_memory_remembers", "[map_memory]" )
+{
+    map_memory memory;
+    memory.memorize_symbol( 2, p1, 1 );
+    memory.memorize_symbol( 2, p2, 2 );
+    CHECK( memory.get_symbol( p1 ) == 1 );
+    CHECK( memory.get_symbol( p2 ) == 2 );
+}
+
+TEST_CASE( "map_memory_limited", "[map_memory]" )
+{
+    map_memory memory;
+    memory.memorize_symbol( 2, p1, 1 );
+    memory.memorize_symbol( 2, p2, 2 );
+    memory.memorize_symbol( 2, p3, 3 );
+    CHECK( memory.get_symbol( p1 ) == 0 );
+}
+
+TEST_CASE( "map_memory_overwrites", "[map_memory]" )
+{
+    map_memory memory;
+    memory.memorize_symbol( 2, p1, 1 );
+    memory.memorize_symbol( 2, p2, 2 );
+    memory.memorize_symbol( 2, p2, 3 );
+    CHECK( memory.get_symbol( p1 ) == 1 );
+    CHECK( memory.get_symbol( p2 ) == 3 );
+}
+
+TEST_CASE( "map_memory_erases_lru", "[map_memory]" )
+{
+    map_memory memory;
+    memory.memorize_symbol( 2, p1, 1 );
+    memory.memorize_symbol( 2, p2, 2 );
+    memory.memorize_symbol( 2, p1, 1 );
+    memory.memorize_symbol( 2, p3, 3 );
+    CHECK( memory.get_symbol( p1 ) == 1 );
+    CHECK( memory.get_symbol( p2 ) == 0 );
+    CHECK( memory.get_symbol( p3 ) == 3 );
+}
+
+TEST_CASE( "map_memory_survives_save_lod", "[map_memory]" )
+{
+    map_memory memory;
+    memory.memorize_symbol( 2, p1, 1 );
+    memory.memorize_symbol( 2, p2, 2 );
+
+    // Save and reload
+    std::ostringstream jsout_s;
+    JsonOut jsout( jsout_s );
+    jsout.start_object( "m" );
+    memory.store( jsout );
+    jsout.end_object();
+
+    INFO( "Json was: " << jsout_s.str() );
+    std::istringstream jsin_s( jsout_s.str() );
+    JsonIn jsin( jsin_s );
+    map_memory memory2;
+    JsonObject json = jsin.get_object();
+    memory2.load( json );
+
+    memory.memorize_symbol( 2, p3, 3 );
+    memory2.memorize_symbol( 2, p3, 3 );
+    CHECK( memory.get_symbol( p1 ) == memory2.get_symbol( p1 ) );
+    CHECK( memory.get_symbol( p2 ) == memory2.get_symbol( p2 ) );
+    CHECK( memory.get_symbol( p3 ) == memory2.get_symbol( p3 ) );
+}