Based on christos@NetBSD's patch

--- shell.c.christos    2014-01-14 08:04:32.000000000 -0500
+++ shell.c     2014-09-25 16:11:51.000000000 -0400
@@ -229,6 +229,7 @@
 #else
 int posixly_correct = 0;       /* Non-zero means posix.2 superset. */
 #endif
+int import_functions = IMPORT_FUNCTIONS_DEF;      /* Import functions from environment */
 
 /* Some long-winded argument names.  These are obviously new. */
 #define Int 1
@@ -248,6 +249,7 @@
   { "help", Int, &want_initial_help, (char **)0x0 },
   { "init-file", Charp, (int *)0x0, &bashrc_file },
   { "login", Int, &make_login_shell, (char **)0x0 },
+  { "import-functions", Int, &import_functions, (char **)0x0 },
   { "noediting", Int, &no_line_editing, (char **)0x0 },
   { "noprofile", Int, &no_profile, (char **)0x0 },
   { "norc", Int, &no_rc, (char **)0x0 },

--- variables.c.orig	2014-09-28 11:15:53.189768951 -0500
+++ variables.c	2014-09-28 11:27:07.250722694 -0500
@@ -110,6 +110,7 @@ extern time_t shell_start_time;
 extern int assigning_in_environment;
 extern int executing_builtin;
 extern int funcnest_max;
+extern int import_functions;
 
 #if defined (READLINE)
 extern int no_line_editing;
@@ -328,6 +329,7 @@ initialize_shell_variables (env, privmod
   char *name, *string, *temp_string;
   int c, char_index, string_index, string_length, ro;
   SHELL_VAR *temp_var;
+  int skipped_import;
 
   create_variable_tables ();
 
@@ -352,9 +354,12 @@ initialize_shell_variables (env, privmod
 
       temp_var = (SHELL_VAR *)NULL;
 
+      skipped_import = 0;
+reval:
+
       /* If exported function, define it now.  Don't import functions from
 	 the environment in privileged mode. */
-      if (privmode == 0 && read_but_dont_execute == 0 && 
+      if (skipped_import == 0 && privmode == 0 && read_but_dont_execute == 0 && 
           STREQN (BASHFUNC_PREFIX, name, BASHFUNC_PREFLEN) &&
           STREQ (BASHFUNC_SUFFIX, name + char_index - BASHFUNC_SUFFLEN) &&
 	  STREQN ("() {", string, 4))
@@ -367,6 +372,12 @@ initialize_shell_variables (env, privmod
 	  tname = name + BASHFUNC_PREFLEN;	/* start of func name */
 	  tname[namelen] = '\0';		/* now tname == func name */
 
+	  if (!import_functions && !interactive_shell) {
+		  skipped_import = 1;
+		  report_error (_("Skipping importing function definition for `%s': --import-functions required."), tname);
+		  goto reval;
+	  }
+
 	  string_length = strlen (string);
 	  temp_string = (char *)xmalloc (namelen + string_length + 2);