diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index d2c895a6fb..bf5873edb1 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -2939,7 +2939,7 @@ heap_page_is_all_visible(Relation rel, Buffer buf,
 /*
  * Compute the number of parallel worker processes to request.  Both index
  * vacuum and index cleanup can be executed with parallel workers.  The
- * relation size of the table don't affect the parallel degree for now.
+ * relation size of the table doesn't affect the parallel degree for now.
  *
  * nrequested is the number of parallel workers that user requested.  If
  * nrequested is 0, we compute the parallel degree based on nindexes, that is
@@ -3365,6 +3365,7 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
 	VacuumPageHit = 0;
 	VacuumPageMiss = 0;
 	VacuumPageDirty = 0;
+	VacuumCostBalanceLocal = 0;
 	VacuumSharedCostBalance = &(lvshared->cost_balance);
 	VacuumActiveNWorkers = &(lvshared->active_nworkers);
 
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 1cd77e79d2..c645d4463f 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -435,7 +435,9 @@ vacuum(List *relations, VacuumParams *params,
 		VacuumPageHit = 0;
 		VacuumPageMiss = 0;
 		VacuumPageDirty = 0;
+		VacuumCostBalanceLocal = 0;
 		VacuumSharedCostBalance = NULL;
+		VacuumActiveNWorkers = NULL;
 
 		/*
 		 * Loop to process each selected relation.
diff --git a/src/test/regress/expected/vacuum.out b/src/test/regress/expected/vacuum.out
index 22cca70687..774ff2fc7c 100644
--- a/src/test/regress/expected/vacuum.out
+++ b/src/test/regress/expected/vacuum.out
@@ -107,6 +107,8 @@ VACUUM (PARALLEL 2) pvactst;
 -- VACUUM invokes parallel bulk-deletion
 UPDATE pvactst SET i = i WHERE i < 1000;
 VACUUM (PARALLEL 2) pvactst;
+UPDATE pvactst SET i = i WHERE i < 1000;
+VACUUM (PARALLEL 0) pvactst; -- disable parallel vacuum
 VACUUM (PARALLEL -1) pvactst; -- error
 ERROR:  parallel vacuum degree must be between 0 and 1024
 LINE 1: VACUUM (PARALLEL -1) pvactst;
diff --git a/src/test/regress/sql/vacuum.sql b/src/test/regress/sql/vacuum.sql
index d6859a5bc9..fbd364d7d0 100644
--- a/src/test/regress/sql/vacuum.sql
+++ b/src/test/regress/sql/vacuum.sql
@@ -93,6 +93,9 @@ VACUUM (PARALLEL 2) pvactst;
 UPDATE pvactst SET i = i WHERE i < 1000;
 VACUUM (PARALLEL 2) pvactst;
 
+UPDATE pvactst SET i = i WHERE i < 1000;
+VACUUM (PARALLEL 0) pvactst; -- disable parallel vacuum
+
 VACUUM (PARALLEL -1) pvactst; -- error
 VACUUM (PARALLEL 2, INDEX_CLEANUP FALSE) pvactst;
 VACUUM (PARALLEL 2, FULL TRUE) pvactst; -- error, cannot use both PARALLEL and FULL