diff --git a/src/test/modules/injection_points/expected/syscache-update-pruned.out b/src/test/modules/injection_points/expected/syscache-update-pruned.out
index 5dc5a1ddc5e..9a9683bb496 100644
--- a/src/test/modules/injection_points/expected/syscache-update-pruned.out
+++ b/src/test/modules/injection_points/expected/syscache-update-pruned.out
@@ -7,7 +7,7 @@ step at2:
 		FOR EACH ROW EXECUTE PROCEDURE suppress_redundant_updates_trigger();
  <waiting ...>
 step waitprunable4: CALL vactest.wait_prunable();
-step vac4: VACUUM pg_class;
+step vac4: VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;
 step grant1: GRANT SELECT ON vactest.orig50 TO PUBLIC; <waiting ...>
 step wakeinval4: 
 	SELECT FROM injection_points_detach('AtEOXact_Inval-with-transInvalInfo');
@@ -30,7 +30,7 @@ step at2:
 		FOR EACH ROW EXECUTE PROCEDURE suppress_redundant_updates_trigger();
  <waiting ...>
 step waitprunable4: CALL vactest.wait_prunable();
-step vac4: VACUUM pg_class;
+step vac4: VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;
 step grant1: GRANT SELECT ON vactest.orig50 TO PUBLIC; <waiting ...>
 step wakeinval4: 
 	SELECT FROM injection_points_detach('AtEOXact_Inval-with-transInvalInfo');
@@ -61,7 +61,7 @@ step mkrels4:
 
 step r3: ROLLBACK;
 step waitprunable4: CALL vactest.wait_prunable();
-step vac4: VACUUM pg_class;
+step vac4: VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;
 step grant1: GRANT SELECT ON vactest.orig50 TO PUBLIC; <waiting ...>
 step wakeinval4: 
 	SELECT FROM injection_points_detach('AtEOXact_Inval-with-transInvalInfo');
diff --git a/src/test/modules/injection_points/expected/syscache-update-pruned_1.out b/src/test/modules/injection_points/expected/syscache-update-pruned_1.out
index b18857c902e..64c39d708bd 100644
--- a/src/test/modules/injection_points/expected/syscache-update-pruned_1.out
+++ b/src/test/modules/injection_points/expected/syscache-update-pruned_1.out
@@ -7,7 +7,7 @@ step at2:
 		FOR EACH ROW EXECUTE PROCEDURE suppress_redundant_updates_trigger();
  <waiting ...>
 step waitprunable4: CALL vactest.wait_prunable();
-step vac4: VACUUM pg_class;
+step vac4: VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;
 step grant1: GRANT SELECT ON vactest.orig50 TO PUBLIC; <waiting ...>
 step wakeinval4: 
 	SELECT FROM injection_points_detach('AtEOXact_Inval-with-transInvalInfo');
@@ -29,7 +29,7 @@ step at2:
 		FOR EACH ROW EXECUTE PROCEDURE suppress_redundant_updates_trigger();
  <waiting ...>
 step waitprunable4: CALL vactest.wait_prunable();
-step vac4: VACUUM pg_class;
+step vac4: VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;
 step grant1: GRANT SELECT ON vactest.orig50 TO PUBLIC; <waiting ...>
 step wakeinval4: 
 	SELECT FROM injection_points_detach('AtEOXact_Inval-with-transInvalInfo');
@@ -59,7 +59,7 @@ step mkrels4:
 
 step r3: ROLLBACK;
 step waitprunable4: CALL vactest.wait_prunable();
-step vac4: VACUUM pg_class;
+step vac4: VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;
 step grant1: GRANT SELECT ON vactest.orig50 TO PUBLIC; <waiting ...>
 step wakeinval4: 
 	SELECT FROM injection_points_detach('AtEOXact_Inval-with-transInvalInfo');
diff --git a/src/test/modules/injection_points/regress_injection.c b/src/test/modules/injection_points/regress_injection.c
index 422f4168935..7bba1c97d0f 100644
--- a/src/test/modules/injection_points/regress_injection.c
+++ b/src/test/modules/injection_points/regress_injection.c
@@ -17,7 +17,9 @@
 #include "access/table.h"
 #include "fmgr.h"
 #include "miscadmin.h"
+#include "postmaster/autovacuum.h"
 #include "storage/procarray.h"
+#include "utils/rel.h"
 #include "utils/xid8.h"
 
 /*
@@ -28,11 +30,12 @@
  * that.  For the causes of backward movement, see
  * postgr.es/m/CAEze2Wj%2BV0kTx86xB_YbyaqTr5hnE_igdWAwuhSyjXBYscf5-Q%40mail.gmail.com
  * and the header comment for ComputeXidHorizons().  One can assume this
- * doesn't move backward if one arranges for concurrent activity not to reach
- * AbortTransaction() and not to allocate an XID while connected to another
- * database.  Non-runningcheck tests can control most concurrent activity,
- * except autovacuum and the isolationtester control connection.  Neither
- * allocates XIDs, and AbortTransaction() in those would justify test failure.
+ * doesn't move backward if one (a) passes a shared catalog as the argument
+ * and (b) arranges for concurrent activity not to reach AbortTransaction().
+ * Non-runningcheck tests can control most concurrent activity, except
+ * autovacuum and the isolationtester control connection.  AbortTransaction()
+ * in those would justify test failure.  Seeing autoanalyze can allocate an
+ * XID in any database, (a) ensures we'll consistently not ignore those XIDs.
  */
 PG_FUNCTION_INFO_V1(removable_cutoff);
 Datum
@@ -47,6 +50,10 @@ removable_cutoff(PG_FUNCTION_ARGS)
 	if (!PG_ARGISNULL(0))
 		rel = table_open(PG_GETARG_OID(0), AccessShareLock);
 
+	if (!rel->rd_rel->relisshared && autovacuum_start_daemon)
+		elog(WARNING,
+			 "removable_cutoff(non-shared-rel) can move backward under autovacuum=on");
+
 	/*
 	 * No lock or snapshot necessarily prevents oldestXid from advancing past
 	 * "xid" while this function runs.  That concerns us only in that we must
diff --git a/src/test/modules/injection_points/specs/syscache-update-pruned.spec b/src/test/modules/injection_points/specs/syscache-update-pruned.spec
index b48e897431e..086d084de25 100644
--- a/src/test/modules/injection_points/specs/syscache-update-pruned.spec
+++ b/src/test/modules/injection_points/specs/syscache-update-pruned.spec
@@ -53,10 +53,12 @@ setup
 		barrier := pg_current_xact_id();
 		-- autovacuum worker RelationCacheInitializePhase3() or the
 		-- isolationtester control connection might hold a snapshot that
-		-- limits pruning.  Sleep until that clears.
+		-- limits pruning.  Sleep until that clears.  See comments at
+		-- removable_cutoff() for why we pass a shared catalog rather than
+		-- pg_class, the table we'll prune.
 		LOOP
 			ROLLBACK;  -- release MyProc->xmin, which could be the oldest
-			cutoff := removable_cutoff('pg_class');
+			cutoff := removable_cutoff('pg_database');
 			EXIT WHEN cutoff >= barrier;
 			RAISE LOG 'removable cutoff %; waiting for %', cutoff, barrier;
 			PERFORM pg_sleep(.1);
@@ -64,9 +66,24 @@ setup
 	END
 	$$;
 }
-setup	{ CALL vactest.wait_prunable();  -- maximize next two VACUUMs }
+# Eliminate HEAPTUPLE_DEAD and HEAPTUPLE_RECENTLY_DEAD from pg_class.
+# Minimize free space.
+#
+# If we kept HEAPTUPLE_RECENTLY_DEAD, step vac4 could prune what we missed,
+# breaking some permutation assumptions.  Specifically, the next pg_class
+# tuple could end up in free space we failed to liberate here, instead of
+# going in the specific free space vac4 intended to liberate for it.
+setup	{ CALL vactest.wait_prunable();  -- maximize VACUUM FULL }
 setup	{ VACUUM FULL pg_class;  -- reduce free space }
-setup	{ VACUUM FREEZE pg_class;  -- populate fsm etc. }
+# Remove the one tuple that VACUUM FULL makes dead, a tuple pertaining to
+# pg_class itself.  Populate the FSM for pg_class.
+#
+# wait_prunable waits for snapshots that would thwart pruning, while FREEZE
+# waits for buffer pins that would thwart pruning.  DISABLE_PAGE_SKIPPING
+# isn't actually needed, but other pruning-dependent tests use it.  If those
+# tests remove it, remove it here.
+setup	{ CALL vactest.wait_prunable();  -- maximize lazy VACUUM }
+setup	{ VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class;  -- fill fsm etc. }
 setup
 {
 	SELECT FROM vactest.mkrels('orig', 1, 49);
@@ -115,7 +132,8 @@ step r3		{ ROLLBACK; }
 # Non-blocking actions.
 session s4
 step waitprunable4	{ CALL vactest.wait_prunable(); }
-step vac4		{ VACUUM pg_class; }
+# Eliminate HEAPTUPLE_DEAD.  See above discussion of FREEZE.
+step vac4		{ VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) pg_class; }
 # Reuse the lp that s1 is waiting to change.  I've observed reuse at the 1st
 # or 18th CREATE, so create excess.
 step mkrels4	{