diff --git a/source/shell/shell.c b/source/shell/shell.c
index feb0b44f..260d6135 100644
--- a/source/shell/shell.c
+++ b/source/shell/shell.c
@@ -8,6 +8,7 @@ SHELL.C
 #include "shell.h"
 #include "errors.h"
 #include "tag_files.h"
+#include "files.h"
 #include "real_math.h"
 #include "game_state.h"
 #include "rasterizer.h"
@@ -36,6 +37,9 @@ boolean shell_initialize(
 		
 		errors_initialize();
 		tag_files_open();
+		/* port: Custom Edition maps live in custom_maps, beside maps.
+		Make that folder when this launch does not already have it. */
+		directory_create("custom_maps");
 		real_math_initialize();
 		game_state_initialize();
 		
diff --git a/source/tag_files/files.c b/source/tag_files/files.c
index b6280dfc..048be1b1 100644
--- a/source/tag_files/files.c
+++ b/source/tag_files/files.c
@@ -291,6 +291,25 @@ void directory_create_or_delete_contents(
 	return;
 }
 
+/* port: make the folder when it is missing. An existing folder is left
+alone, including whatever is already in it. */
+void directory_create(
+	const char *directory_name)
+{
+	struct file_reference directory;
+	struct file_reference_info *info = (struct file_reference_info *)&directory;
+
+	memset(info, 0, FILE_REFERENCE_SIZE);
+	info->signature = FILE_REFERENCE_SIGNATURE;
+	info->location = NONE;
+
+	file_reference_add_directory(&directory, directory_name);
+	if (!file_exists(&directory))
+		file_create(&directory);
+
+	return;
+}
+
 boolean datastore_read(
 	const char *file_name,
 	const char *field_name,
diff --git a/source/tag_files/files.h b/source/tag_files/files.h
index b8b23161..77559987 100644
--- a/source/tag_files/files.h
+++ b/source/tag_files/files.h
@@ -146,6 +146,7 @@ char *file_reference_get_name(const struct file_reference *reference, unsigned l
 boolean file_references_equal(const struct file_reference *reference0, const struct file_reference *reference1);
 struct file_reference *file_reference_create_from_path(struct file_reference *reference, const char *path, boolean is_directory);
 void directory_create_or_delete_contents(const char *directory_name);
+void directory_create(const char *directory_name);
 boolean datastore_read(const char *file_name, const char *field_name, long length, void *data);
 boolean datastore_write(const char *file_name, const char *field_name, long length, const void *data);