diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 174c72a14b..1342c18c74 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -588,7 +588,7 @@ ProcessClientWriteInterrupt(bool blocked)
 		{
 			/*
 			 * Don't mess with whereToSendOutput if ProcessInterrupts wouldn't
-			 * do anything.
+			 * service ProcDiePending.
 			 */
 			if (InterruptHoldoffCount == 0 && CritSectionCount == 0)
 			{
@@ -3026,6 +3026,12 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
  * If an interrupt condition is pending, and it's safe to service it,
  * then clear the flag and accept the interrupt.  Called only when
  * InterruptPending is true.
+ *
+ * Note: if INTERRUPTS_CAN_BE_PROCESSED() is true, then ProcessInterrupts
+ * is guaranteed to clear the InterruptPending flag before returning.
+ * (This is not the same as guaranteeing that it's still clear when we
+ * return; another interrupt could have arrived.  But we promise that
+ * any pre-existing one will have been serviced.)
  */
 void
 ProcessInterrupts(void)
@@ -3130,7 +3136,11 @@ ProcessInterrupts(void)
 	{
 		/*
 		 * Re-arm InterruptPending so that we process the cancel request as
-		 * soon as we're done reading the message.
+		 * soon as we're done reading the message.  (XXX this is seriously
+		 * ugly: it complicates INTERRUPTS_CAN_BE_PROCESSED(), and it means we
+		 * can't use that macro directly as the initial test in this function,
+		 * meaning that this code also creates opportunities for other bugs to
+		 * appear.)
 		 */
 		InterruptPending = true;
 	}
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 72e3352398..6e80065374 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -57,6 +57,15 @@
  * allowing die interrupts: HOLD_CANCEL_INTERRUPTS() and
  * RESUME_CANCEL_INTERRUPTS().
  *
+ * Note that ProcessInterrupts() has also acquired a number of tasks that
+ * do not necessarily cause a query-cancel-or-die response.  Hence, it's
+ * possible that it will just clear InterruptPending and return.
+ *
+ * INTERRUPTS_PENDING_CONDITION() can be checked to see whether an
+ * interrupt needs to be serviced, without trying to do so immediately.
+ * Some callers are also interested in INTERRUPTS_CAN_BE_PROCESSED(),
+ * which tells whether ProcessInterrupts is sure to clear the interrupt.
+ *
  * Special mechanisms are used to let an interrupt be accepted when we are
  * waiting for a lock or when we are waiting for command input (but, of
  * course, only if the interrupt holdoff counter is zero).  See the
@@ -94,24 +103,27 @@ extern PGDLLIMPORT volatile uint32 CritSectionCount;
 /* in tcop/postgres.c */
 extern void ProcessInterrupts(void);
 
+/* Test whether an interrupt is pending */
 #ifndef WIN32
+#define INTERRUPTS_PENDING_CONDITION() \
+	(unlikely(InterruptPending))
+#else
+#define INTERRUPTS_PENDING_CONDITION() \
+	(unlikely(UNBLOCKED_SIGNAL_QUEUE()) ? pgwin32_dispatch_queued_signals() : 0, \
+	 unlikely(InterruptPending))
+#endif
 
+/* Service interrupt, if one is pending and it's safe to service it now */
 #define CHECK_FOR_INTERRUPTS() \
 do { \
-	if (unlikely(InterruptPending)) \
+	if (INTERRUPTS_PENDING_CONDITION()) \
 		ProcessInterrupts(); \
 } while(0)
-#else							/* WIN32 */
-
-#define CHECK_FOR_INTERRUPTS() \
-do { \
-	if (unlikely(UNBLOCKED_SIGNAL_QUEUE())) \
-		pgwin32_dispatch_queued_signals(); \
-	if (unlikely(InterruptPending)) \
-		ProcessInterrupts(); \
-} while(0)
-#endif							/* WIN32 */
 
+/* Is ProcessInterrupts() guaranteed to clear InterruptPending? */
+#define INTERRUPTS_CAN_BE_PROCESSED() \
+	(InterruptHoldoffCount == 0 && CritSectionCount == 0 && \
+	 QueryCancelHoldoffCount == 0)
 
 #define HOLD_INTERRUPTS()  (InterruptHoldoffCount++)