diff --git a/src/pl/plpython/plpy_main.c b/src/pl/plpython/plpy_main.c
index 3c2ebfa..059adfa 100644
*** a/src/pl/plpython/plpy_main.c
--- b/src/pl/plpython/plpy_main.c
*************** static void PLy_init_interp(void);
*** 63,69 ****
  static PLyExecutionContext *PLy_push_execution_context(void);
  static void PLy_pop_execution_context(void);
  
! static const int plpython_python_version = PY_MAJOR_VERSION;
  
  /* initialize global variables */
  PyObject   *PLy_interp_globals = NULL;
--- 63,70 ----
  static PLyExecutionContext *PLy_push_execution_context(void);
  static void PLy_pop_execution_context(void);
  
! static int *plpython_version_bitmask_ptr = NULL;
! static int	plpython_version_bitmask = 0;
  
  /* initialize global variables */
  PyObject   *PLy_interp_globals = NULL;
*************** static PLyExecutionContext *PLy_executio
*** 75,102 ****
  void
  _PG_init(void)
  {
! 	/* Be sure we do initialization only once (should be redundant now) */
! 	static bool inited = false;
  	const int **version_ptr;
  
! 	if (inited)
! 		return;
  
! 	/* Be sure we don't run Python 2 and 3 in the same session (might crash) */
  	version_ptr = (const int **) find_rendezvous_variable("plpython_python_version");
! 	if (!(*version_ptr))
! 		*version_ptr = &plpython_python_version;
! 	else
! 	{
! 		if (**version_ptr != plpython_python_version)
! 			ereport(FATAL,
! 					(errmsg("Python major version mismatch in session"),
! 					 errdetail("This session has previously used Python major version %d, and it is now attempting to use Python major version %d.",
! 							   **version_ptr, plpython_python_version),
! 					 errhint("Start a new session to use a different Python major version.")));
! 	}
  
! 	pg_bindtextdomain(TEXTDOMAIN);
  
  #if PY_MAJOR_VERSION >= 3
  	PyImport_AppendInittab("plpy", PyInit_plpy);
--- 76,144 ----
  void
  _PG_init(void)
  {
! 	int		  **bitmask_ptr;
  	const int **version_ptr;
  
! 	/*
! 	 * Set up a shared bitmask variable telling which Python version(s) are
! 	 * loaded into this process's address space.  If there's more than one, we
! 	 * cannot call into libpython for fear of causing crashes.  But postpone
! 	 * the actual failure for later, so that operations like pg_restore can
! 	 * load more than one plpython library so long as they don't try to do
! 	 * anything much with the language.
! 	 */
! 	bitmask_ptr = (int **) find_rendezvous_variable("plpython_version_bitmask");
! 	if (!(*bitmask_ptr))		/* am I the first? */
! 		*bitmask_ptr = &plpython_version_bitmask;
! 	/* Retain pointer to the agreed-on shared variable ... */
! 	plpython_version_bitmask_ptr = *bitmask_ptr;
! 	/* ... and announce my presence */
! 	*plpython_version_bitmask_ptr |= (1 << PY_MAJOR_VERSION);
  
! 	/*
! 	 * This should be safe even in the presence of conflicting plpythons, and
! 	 * it's necessary to do it here for the next error to be localized.
! 	 */
! 	pg_bindtextdomain(TEXTDOMAIN);
! 
! 	/*
! 	 * We used to have a scheme whereby PL/Python would fail immediately if
! 	 * loaded into a session in which a conflicting libpython is already
! 	 * present.  We don't like to do that anymore, but it seems possible that
! 	 * a plpython library adhering to the old convention is present in the
! 	 * session, in which case we have to fail.
! 	 */
  	version_ptr = (const int **) find_rendezvous_variable("plpython_python_version");
! 	if ((*version_ptr) != NULL)
! 		ereport(FATAL,
! 				(errmsg("Python major version mismatch in session"),
! 				 errdetail("This session has previously used Python major version %d, and it is now attempting to use Python major version %d.",
! 						   **version_ptr, PY_MAJOR_VERSION),
! 				 errhint("Start a new session to use a different Python major version.")));
! }
  
! /*
!  * Perform one-time setup of PL/Python, after checking for a conflict
!  * with other versions of Python.
!  */
! static void
! PLy_initialize(void)
! {
! 	static bool inited = false;
! 
! 	/*
! 	 * Check for multiple Python libraries before actively doing anything with
! 	 * libpython.  This must be repeated on each entry to PL/Python, in case a
! 	 * conflicting library got loaded since we last looked.
! 	 */
! 	if (*plpython_version_bitmask_ptr != (1 << PY_MAJOR_VERSION))
! 		ereport(ERROR,
! 				(errmsg("multiple Python libraries are present in session"),
! 				 errdetail("Only one Python major version can be used in one session.")));
! 
! 	/* The rest should only be done once per session */
! 	if (inited)
! 		return;
  
  #if PY_MAJOR_VERSION >= 3
  	PyImport_AppendInittab("plpy", PyInit_plpy);
*************** _PG_init(void)
*** 120,126 ****
  }
  
  /*
!  * This should only be called once from _PG_init. Initialize the Python
   * interpreter and global data.
   */
  static void
--- 162,168 ----
  }
  
  /*
!  * This should be called only once, from PLy_initialize. Initialize the Python
   * interpreter and global data.
   */
  static void
*************** plpython_validator(PG_FUNCTION_ARGS)
*** 155,163 ****
  		PG_RETURN_VOID();
  
  	if (!check_function_bodies)
- 	{
  		PG_RETURN_VOID();
! 	}
  
  	/* Get the new function's pg_proc entry */
  	tuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcoid));
--- 197,206 ----
  		PG_RETURN_VOID();
  
  	if (!check_function_bodies)
  		PG_RETURN_VOID();
! 
! 	/* Do this only after making sure we need to do something */
! 	PLy_initialize();
  
  	/* Get the new function's pg_proc entry */
  	tuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcoid));
*************** plpython_call_handler(PG_FUNCTION_ARGS)
*** 191,196 ****
--- 234,241 ----
  	PLyExecutionContext *exec_ctx;
  	ErrorContextCallback plerrcontext;
  
+ 	PLy_initialize();
+ 
  	/* Note: SPI_finish() happens in plpy_exec.c, which is dubious design */
  	if (SPI_connect() != SPI_OK_CONNECT)
  		elog(ERROR, "SPI_connect failed");
*************** plpython_inline_handler(PG_FUNCTION_ARGS
*** 266,271 ****
--- 311,318 ----
  	PLyExecutionContext *exec_ctx;
  	ErrorContextCallback plerrcontext;
  
+ 	PLy_initialize();
+ 
  	/* Note: SPI_finish() happens in plpy_exec.c, which is dubious design */
  	if (SPI_connect() != SPI_OK_CONNECT)
  		elog(ERROR, "SPI_connect failed");