diff --git a/files.c b/files.c
index 9b2f532..5a13b49 100644
--- a/files.c
+++ b/files.c
@@ -553,11 +553,12 @@ game features require version 0x%08lx", requested_glulx_version, VersionNum);
     sf_put((Out_Size >> 16));
     sf_put((Out_Size >> 8));
     sf_put((Out_Size));
-    /* ENDMEM, which is also game file size */
-    sf_put((Out_Size >> 24));
-    sf_put((Out_Size >> 16));
-    sf_put((Out_Size >> 8));
-    sf_put((Out_Size));
+    /* ENDMEM, which the game file size plus MEMORY_MAP_EXTENSION */
+    i = Out_Size + MEMORY_MAP_EXTENSION;
+    sf_put((i >> 24));
+    sf_put((i >> 16));
+    sf_put((i >> 8));
+    sf_put((i));
     /* STACKSIZE */
     sf_put((MAX_STACK_SIZE >> 24));
     sf_put((MAX_STACK_SIZE >> 16));
diff --git a/header.h b/header.h
index 28ca1d1..7358e33 100644
--- a/header.h
+++ b/header.h
@@ -2409,7 +2409,7 @@ extern int MAX_QTEXT_SIZE,  MAX_SYMBOLS,    HASH_TAB_SIZE,   MAX_DICT_ENTRIES,
 extern int32 MAX_STATIC_STRINGS, MAX_ZCODE_SIZE, MAX_LINK_DATA_SIZE,
            MAX_TRANSCRIPT_SIZE,  MAX_INDIV_PROP_TABLE_SIZE,
            MAX_NUM_STATIC_STRINGS, MAX_UNICODE_CHARS,
-           MAX_STACK_SIZE;
+           MAX_STACK_SIZE, MEMORY_MAP_EXTENSION;
 
 extern int32 MAX_OBJ_PROP_COUNT, MAX_OBJ_PROP_TABLE_SIZE;
 extern int MAX_LOCAL_VARIABLES, MAX_GLOBAL_VARIABLES;
diff --git a/memory.c b/memory.c
index a94f98b..1ec8baa 100644
--- a/memory.c
+++ b/memory.c
@@ -176,6 +176,7 @@ int NUM_ATTR_BYTES;
 int32 MAX_NUM_STATIC_STRINGS;
 int32 MAX_UNICODE_CHARS;
 int32 MAX_STACK_SIZE;
+int32 MEMORY_MAP_EXTENSION;
 int ALLOC_CHUNK_SIZE;
 
 /* The way memory sizes are set causes great nuisance for those parameters
@@ -220,6 +221,9 @@ static void list_memory_sizes(void)
       printf("|  %25s = %-7d |\n","MAX_LOCAL_VARIABLES",MAX_LOCAL_VARIABLES);
     printf("|  %25s = %-7d |\n","MAX_LOW_STRINGS",MAX_LOW_STRINGS);
     if (glulx_mode)
+      printf("|  %25s = %-7d |\n","MEMORY_MAP_EXTENSION",
+        MEMORY_MAP_EXTENSION);
+    if (glulx_mode)
       printf("|  %25s = %-7d |\n","MAX_NUM_STATIC_STRINGS",
         MAX_NUM_STATIC_STRINGS);
     printf("|  %25s = %-7d |\n","MAX_OBJECTS",MAX_OBJECTS);
@@ -418,6 +422,7 @@ extern void set_memory_sizes(int size_flag)
     NUM_ATTR_BYTES_z = 6;
     NUM_ATTR_BYTES_g = 7;
     MAX_UNICODE_CHARS = 64;
+    MEMORY_MAP_EXTENSION = 0;
     /* We estimate the default Glulx stack size at 4096. That's about
        enough for 90 nested function calls with 8 locals each -- the
        same capacity as the Z-Spec's suggestion for Z-machine stack
@@ -700,6 +705,13 @@ static void explain_parameter(char *command)
   during gameplay. (Glulx only)\n");
         return;
     }
+    if (strcmp(command,"MEMORY_MAP_EXTENSION")==0)
+    {
+        printf(
+"  MEMORY_MAP_EXTENSION is the number of bytes (all zeroes) to map into \n\
+  memory after the game file. (Glulx only)\n");
+        return;
+    }
 
     printf("No such memory setting as \"%s\"\n",command);
 
@@ -845,6 +857,12 @@ extern void memory_command(char *command)
                 /* Adjust up to a 256-byte boundary. */
                 MAX_STACK_SIZE = (MAX_STACK_SIZE + 0xFF) & (~0xFF);
             }
+            if (strcmp(command,"MEMORY_MAP_EXTENSION")==0)
+            {
+                MEMORY_MAP_EXTENSION=j, flag=1;
+                /* Adjust up to a 256-byte boundary. */
+                MEMORY_MAP_EXTENSION = (MEMORY_MAP_EXTENSION + 0xFF) & (~0xFF);
+            }
 
             if (flag==0)
                 printf("No such memory setting as \"%s\"\n", command);