diff --git a/doc/src/sgml/spi.sgml b/doc/src/sgml/spi.sgml
index 47f4b5b4317..5c36b534902 100644
--- a/doc/src/sgml/spi.sgml
+++ b/doc/src/sgml/spi.sgml
@@ -742,7 +742,9 @@ int SPI_execute_extended(const char *<parameter>command</parameter>,
     <listitem>
      <para>
       <literal>true</literal> allows non-atomic execution of CALL and DO
-      statements
+      statements (but this field is ignored unless
+      the <symbol>SPI_OPT_NONATOMIC</symbol> flag was passed
+      to <function>SPI_connect_ext</function>)
      </para>
     </listitem>
    </varlistentry>
@@ -1883,7 +1885,9 @@ int SPI_execute_plan_extended(SPIPlanPtr <parameter>plan</parameter>,
     <listitem>
      <para>
       <literal>true</literal> allows non-atomic execution of CALL and DO
-      statements
+      statements (but this field is ignored unless
+      the <symbol>SPI_OPT_NONATOMIC</symbol> flag was passed
+      to <function>SPI_connect_ext</function>)
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 1edbd4353f6..ffb7fcadf73 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -2398,6 +2398,7 @@ _SPI_execute_plan(SPIPlanPtr plan, const SPIExecuteOptions *options,
 	uint64		my_processed = 0;
 	SPITupleTable *my_tuptable = NULL;
 	int			res = 0;
+	bool		allow_nonatomic;
 	bool		pushed_active_snap = false;
 	ResourceOwner plan_owner = options->owner;
 	SPICallbackArg spicallbackarg;
@@ -2405,6 +2406,12 @@ _SPI_execute_plan(SPIPlanPtr plan, const SPIExecuteOptions *options,
 	CachedPlan *cplan = NULL;
 	ListCell   *lc1;
 
+	/*
+	 * We allow nonatomic behavior only if options->allow_nonatomic is set
+	 * *and* the SPI_OPT_NONATOMIC flag was given when connecting.
+	 */
+	allow_nonatomic = options->allow_nonatomic && !_SPI_current->atomic;
+
 	/*
 	 * Setup error traceback support for ereport()
 	 */
@@ -2424,12 +2431,17 @@ _SPI_execute_plan(SPIPlanPtr plan, const SPIExecuteOptions *options,
 	 * snapshot != InvalidSnapshot, read_only = false: use the given snapshot,
 	 * modified by advancing its command ID before each querytree.
 	 *
-	 * snapshot == InvalidSnapshot, read_only = true: use the entry-time
-	 * ActiveSnapshot, if any (if there isn't one, we run with no snapshot).
+	 * snapshot == InvalidSnapshot, read_only = true: do nothing for queries
+	 * that require no snapshot.  For those that do, ensure that a Portal
+	 * snapshot exists; then use that, or use the entry-time ActiveSnapshot if
+	 * that exists and is different.
 	 *
-	 * snapshot == InvalidSnapshot, read_only = false: take a full new
-	 * snapshot for each user command, and advance its command ID before each
-	 * querytree within the command.
+	 * snapshot == InvalidSnapshot, read_only = false: do nothing for queries
+	 * that require no snapshot.  For those that do, ensure that a Portal
+	 * snapshot exists; then, in atomic execution (!allow_nonatomic) take a
+	 * full new snapshot for each user command, and advance its command ID
+	 * before each querytree within the command.  In allow_nonatomic mode we
+	 * just use the Portal snapshot unmodified.
 	 *
 	 * In the first two cases, we can just push the snap onto the stack once
 	 * for the whole plan list.
@@ -2439,6 +2451,7 @@ _SPI_execute_plan(SPIPlanPtr plan, const SPIExecuteOptions *options,
 	 */
 	if (snapshot != InvalidSnapshot)
 	{
+		/* this intentionally tests the options field not the derived value */
 		Assert(!options->allow_nonatomic);
 		if (options->read_only)
 		{
@@ -2584,7 +2597,7 @@ _SPI_execute_plan(SPIPlanPtr plan, const SPIExecuteOptions *options,
 			 * Skip it when doing non-atomic execution, though (we rely
 			 * entirely on the Portal snapshot in that case).
 			 */
-			if (!options->read_only && !options->allow_nonatomic)
+			if (!options->read_only && !allow_nonatomic)
 			{
 				if (pushed_active_snap)
 					PopActiveSnapshot();
@@ -2684,14 +2697,13 @@ _SPI_execute_plan(SPIPlanPtr plan, const SPIExecuteOptions *options,
 				QueryCompletion qc;
 
 				/*
-				 * If the SPI context is atomic, or we were not told to allow
-				 * nonatomic operations, tell ProcessUtility this is an atomic
-				 * execution context.
+				 * If we're not allowing nonatomic operations, tell
+				 * ProcessUtility this is an atomic execution context.
 				 */
-				if (_SPI_current->atomic || !options->allow_nonatomic)
-					context = PROCESS_UTILITY_QUERY;
-				else
+				if (allow_nonatomic)
 					context = PROCESS_UTILITY_QUERY_NONATOMIC;
+				else
+					context = PROCESS_UTILITY_QUERY;
 
 				InitializeQueryCompletion(&qc);
 				ProcessUtility(stmt,
diff --git a/src/pl/plpgsql/src/expected/plpgsql_call.out b/src/pl/plpgsql/src/expected/plpgsql_call.out
index 17235fca912..0a63b1d44ef 100644
--- a/src/pl/plpgsql/src/expected/plpgsql_call.out
+++ b/src/pl/plpgsql/src/expected/plpgsql_call.out
@@ -564,3 +564,53 @@ NOTICE:  inner_p(44)
  
 (1 row)
 
+-- Check that stable functions in CALL see the correct snapshot
+CREATE TABLE t_test (x int);
+INSERT INTO t_test VALUES (0);
+CREATE FUNCTION f_get_x () RETURNS int
+AS $$
+DECLARE l_result int;
+BEGIN
+  SELECT x INTO l_result FROM t_test;
+  RETURN l_result;
+END
+$$ LANGUAGE plpgsql STABLE;
+CREATE PROCEDURE f_print_x (x int)
+AS $$
+BEGIN
+  RAISE NOTICE 'f_print_x(%)', x;
+END
+$$ LANGUAGE plpgsql;
+-- test in non-atomic context
+DO $$
+BEGIN
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+  ROLLBACK;
+END
+$$;
+NOTICE:  f_get_x(1)
+NOTICE:  f_print_x(1)
+NOTICE:  f_get_x(2)
+NOTICE:  f_print_x(2)
+-- test in atomic context
+BEGIN;
+DO $$
+BEGIN
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+END
+$$;
+NOTICE:  f_get_x(1)
+NOTICE:  f_print_x(1)
+NOTICE:  f_get_x(2)
+NOTICE:  f_print_x(2)
+ROLLBACK;
diff --git a/src/pl/plpgsql/src/sql/plpgsql_call.sql b/src/pl/plpgsql/src/sql/plpgsql_call.sql
index 869d021a075..4cbda0382e9 100644
--- a/src/pl/plpgsql/src/sql/plpgsql_call.sql
+++ b/src/pl/plpgsql/src/sql/plpgsql_call.sql
@@ -522,3 +522,53 @@ CREATE FUNCTION f(int) RETURNS int AS $$ SELECT $1 + 2 $$ LANGUAGE sql;
 
 CALL outer_p(42);
 SELECT outer_f(42);
+
+-- Check that stable functions in CALL see the correct snapshot
+
+CREATE TABLE t_test (x int);
+INSERT INTO t_test VALUES (0);
+
+CREATE FUNCTION f_get_x () RETURNS int
+AS $$
+DECLARE l_result int;
+BEGIN
+  SELECT x INTO l_result FROM t_test;
+  RETURN l_result;
+END
+$$ LANGUAGE plpgsql STABLE;
+
+CREATE PROCEDURE f_print_x (x int)
+AS $$
+BEGIN
+  RAISE NOTICE 'f_print_x(%)', x;
+END
+$$ LANGUAGE plpgsql;
+
+-- test in non-atomic context
+DO $$
+BEGIN
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+  ROLLBACK;
+END
+$$;
+
+-- test in atomic context
+BEGIN;
+
+DO $$
+BEGIN
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+  UPDATE t_test SET x = x + 1;
+  RAISE NOTICE 'f_get_x(%)', f_get_x();
+  CALL f_print_x(f_get_x());
+END
+$$;
+
+ROLLBACK;