diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 63b32246174..8670230d48d 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1093,9 +1093,10 @@ SELCT 1/0;<!-- this typo is intentional -->
     implicit <command>ROLLBACK</command> if they failed.  However, there
     are a few DDL commands (such as <command>CREATE DATABASE</command>)
     that cannot be executed inside a transaction block.  If one of
-    these is executed in a pipeline, it will, upon success, force an
-    immediate commit to preserve database consistency.
-    A Sync immediately following one of these has no effect except to
+    these is executed in a pipeline, it will fail unless it is the first
+    command in the pipeline.  Furthermore, upon success it will force an
+    immediate commit to preserve database consistency.  Thus a Sync
+    immediately following one of these commands has no effect except to
     respond with ReadyForQuery.
    </para>
 
@@ -1103,7 +1104,7 @@ SELCT 1/0;<!-- this typo is intentional -->
     When using this method, completion of the pipeline must be determined
     by counting ReadyForQuery messages and waiting for that to reach the
     number of Syncs sent.  Counting command completion responses is
-    unreliable, since some of the commands may not be executed and thus not
+    unreliable, since some of the commands may be skipped and thus not
     produce a completion message.
    </para>
   </sect2>
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 711adc4622c..9e3c6481f44 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -3405,6 +3405,16 @@ PreventInTransactionBlock(bool isTopLevel, const char *stmtType)
 				 errmsg("%s cannot run inside a subtransaction",
 						stmtType)));
 
+	/*
+	 * inside a pipeline that has started an implicit transaction?
+	 */
+	if (MyXactFlags & XACT_FLAGS_PIPELINING)
+		ereport(ERROR,
+				(errcode(ERRCODE_ACTIVE_SQL_TRANSACTION),
+		/* translator: %s represents an SQL statement name */
+				 errmsg("%s cannot be executed within a pipeline",
+						stmtType)));
+
 	/*
 	 * inside a function call?
 	 */
@@ -3494,9 +3504,11 @@ CheckTransactionBlock(bool isTopLevel, bool throwError, const char *stmtType)
  *	a transaction block than when running as single commands.  ANALYZE is
  *	currently the only example.
  *
- *	If this routine returns "false", then the calling statement is
- *	guaranteed that if it completes without error, its results will be
- *	committed immediately.
+ *	If this routine returns "false", then the calling statement is allowed
+ *	to perform internal transaction-commit-and-start cycles; there is not a
+ *	risk of messing up any transaction already in progress.  (Note that this
+ *	is not the identical guarantee provided by PreventInTransactionBlock,
+ *	since we will not force a post-statement commit.)
  *
  *	isTopLevel: passed down from ProcessUtility to determine whether we are
  *	inside a function.
@@ -3514,6 +3526,9 @@ IsInTransactionBlock(bool isTopLevel)
 	if (IsSubTransaction())
 		return true;
 
+	if (MyXactFlags & XACT_FLAGS_PIPELINING)
+		return true;
+
 	if (!isTopLevel)
 		return true;
 
@@ -3521,13 +3536,6 @@ IsInTransactionBlock(bool isTopLevel)
 		CurrentTransactionState->blockState != TBLOCK_STARTED)
 		return true;
 
-	/*
-	 * If we tell the caller we're not in a transaction block, then inform
-	 * postgres.c that it had better commit when the statement is done.
-	 * Otherwise our report could be a lie.
-	 */
-	MyXactFlags |= XACT_FLAGS_NEEDIMMEDIATECOMMIT;
-
 	return false;
 }
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 5bee74363cc..ea7ec2729a9 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -2224,6 +2224,12 @@ exec_execute_message(const char *portal_name, long max_rows)
 			 */
 			CommandCounterIncrement();
 
+			/*
+			 * Set XACT_FLAGS_PIPELINING whenever we complete an Execute
+			 * message without immediately committing the transaction.
+			 */
+			MyXactFlags |= XACT_FLAGS_PIPELINING;
+
 			/*
 			 * Disable statement timeout whenever we complete an Execute
 			 * message.  The next protocol message will start a fresh timeout.
@@ -2239,6 +2245,12 @@ exec_execute_message(const char *portal_name, long max_rows)
 		/* Portal run not complete, so send PortalSuspended */
 		if (whereToSendOutput == DestRemote)
 			pq_putemptymessage('s');
+
+		/*
+		 * Set XACT_FLAGS_PIPELINING whenever we suspend an Execute message,
+		 * too.
+		 */
+		MyXactFlags |= XACT_FLAGS_PIPELINING;
 	}
 
 	/*
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index f00fe4eb582..eb9d6c35d17 100644
--- a/src/include/access/xact.h
+++ b/src/include/access/xact.h
@@ -109,6 +109,13 @@ extern int	MyXactFlags;
  */
 #define XACT_FLAGS_NEEDIMMEDIATECOMMIT			(1U << 2)
 
+/*
+ * XACT_FLAGS_PIPELINING - set when we complete an extended-query-protocol
+ * Execute message.  This is useful for detecting that an implicit transaction
+ * block has been created via pipelining.
+ */
+#define XACT_FLAGS_PIPELINING					(1U << 3)
+
 /*
  *	start- and end-of-transaction callbacks for dynamically loaded modules
  */