diff --git a/src/map.cpp b/src/map.cpp
index 3ed741cfb49b3..76760fb5b6057 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -7332,44 +7332,29 @@ bool tinymap::inbounds( const tripoint &p ) const
 
 // set up a map just long enough scribble on it
 // this tinymap should never, ever get saved
-bool tinymap::fake_load( const furn_id &fur_type, const ter_id &ter_type, const trap_id &trap_type,
-                         int fake_map_z )
+fake_map::fake_map( const furn_id &fur_type, const ter_id &ter_type, const trap_id &trap_type,
+                    const int fake_map_z )
 {
     const tripoint tripoint_below_zero( 0, 0, fake_map_z );
 
-    bool do_terset = true;
     set_abs_sub( tripoint_below_zero );
     for( int gridx = 0; gridx < my_MAPSIZE; gridx++ ) {
         for( int gridy = 0; gridy < my_MAPSIZE; gridy++ ) {
-            const tripoint gridp( gridx, gridy, fake_map_z );
-            submap *tmpsub = MAPBUFFER.lookup_submap( gridp );
-            if( tmpsub == nullptr ) {
-                generate_uniform( gridp, ter_type );
-                do_terset = false;
-                tmpsub = MAPBUFFER.lookup_submap( gridp );
-                if( tmpsub == nullptr ) {
-                    dbg( D_ERROR ) << "failed to generate a fake submap at 0,0,-9 ";
-                    debugmsg( "failed to generate a fake submap at 0,0,-9" );
-                    return false;
-                }
-            }
-            const size_t gridn = get_nonant( gridp );
+            std::unique_ptr<submap> sm = std::make_unique<submap>();
 
-            setsubmap( gridn, tmpsub );
-        }
-    }
+            std::uninitialized_fill_n( &sm->ter[0][0], SEEX * SEEY, ter_type );
+            std::uninitialized_fill_n( &sm->frn[0][0], SEEX * SEEY, fur_type );
+            std::uninitialized_fill_n( &sm->trp[0][0], SEEX * SEEY, trap_type );
+
+            setsubmap( get_nonant( { gridx, gridy, fake_map_z } ), sm.get() );
 
-    for( const tripoint &pos : points_in_rectangle( tripoint_below_zero,
-            tripoint( MAPSIZE * SEEX, MAPSIZE * SEEY, fake_map_z ) ) ) {
-        if( do_terset ) {
-            ter_set( pos, ter_type );
+            temp_submaps_.emplace_back( std::move( sm ) );
         }
-        furn_set( pos, fur_type );
-        trap_set( pos, trap_type );
     }
-    return true;
 }
 
+fake_map::~fake_map() = default;
+
 void map::set_graffiti( const tripoint &p, const std::string &contents )
 {
     if( !inbounds( p ) ) {
diff --git a/src/map.h b/src/map.h
index 65a89eb8d3c65..ba5ab3e96b3f9 100644
--- a/src/map.h
+++ b/src/map.h
@@ -1834,8 +1834,15 @@ class tinymap : public map
     public:
         tinymap( int mapsize = 2, bool zlevels = false );
         bool inbounds( const tripoint &p ) const override;
-        bool fake_load( const furn_id &fur_type, const ter_id &ter_type, const trap_id &trap_type,
-                        int fake_map_z );
 };
 
+class fake_map : public tinymap
+{
+    private:
+        std::vector<std::unique_ptr<submap>> temp_submaps_;
+    public:
+        fake_map( const furn_id &fur_type, const ter_id &ter_type, const trap_id &trap_type,
+                  int fake_map_z );
+        ~fake_map();
+};
 #endif
diff --git a/src/mapgen.cpp b/src/mapgen.cpp
index eb641e5de8e18..4eb206c519909 100644
--- a/src/mapgen.cpp
+++ b/src/mapgen.cpp
@@ -7272,8 +7272,6 @@ std::pair<std::map<ter_id, int>, std::map<furn_id, int>> get_changed_ids_from_up
             const std::string &update_mapgen_id )
 {
     const int fake_map_z = -9;
-    const tripoint tripoint_below_zero( 0, 0, fake_map_z );
-    const tripoint tripoint_fake_map_edge( 23, 23, fake_map_z );
 
     std::map<ter_id, int> terrains;
     std::map<furn_id, int> furnitures;
@@ -7284,10 +7282,8 @@ std::pair<std::map<ter_id, int>, std::map<furn_id, int>> get_changed_ids_from_up
         return std::make_pair( terrains, furnitures );
     }
 
-    tinymap fake_map;
-    if( !fake_map.fake_load( f_null, t_dirt, tr_null, fake_map_z ) ) {
-        return std::make_pair( terrains, furnitures );
-    }
+    ::fake_map fake_map( f_null, t_dirt, tr_null, fake_map_z );
+
     oter_id any = oter_id( "field" );
     // just need a variable here, it doesn't need to be valid
     const regional_settings dummy_settings;
@@ -7296,20 +7292,13 @@ std::pair<std::map<ter_id, int>, std::map<furn_id, int>> get_changed_ids_from_up
                         any, any, 0, dummy_settings, fake_map, any, 0.0f, calendar::turn, nullptr );
 
     if( update_function->second[0]->update_map( fake_md ) ) {
-        for( const tripoint &pos : fake_map.points_in_rectangle( tripoint_below_zero,
-                tripoint_fake_map_edge ) ) {
+        for( const tripoint &pos : fake_map.points_on_zlevel( fake_map_z ) ) {
             ter_id ter_at_pos = fake_map.ter( pos );
             if( ter_at_pos != t_dirt ) {
-                if( terrains.find( ter_at_pos ) == terrains.end() ) {
-                    terrains[ter_at_pos] = 0;
-                }
                 terrains[ter_at_pos] += 1;
             }
             if( fake_map.has_furn( pos ) ) {
                 furn_id furn_at_pos = fake_map.furn( pos );
-                if( furnitures.find( furn_at_pos ) == furnitures.end() ) {
-                    furnitures[furn_at_pos] = 0;
-                }
                 furnitures[furn_at_pos] += 1;
             }
         }