diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index e70243a008..5ff78248e0 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -3217,7 +3217,7 @@ isOtherTempNamespace(Oid namespaceId)
 }
 
 /*
- * isTempNamespaceInUse - is the given namespace owned and actively used
+ * checkTempNamespaceStatus - is the given namespace owned and actively used
  * by a backend?
  *
  * Note: this can be used while scanning relations in pg_class to detect
@@ -3225,8 +3225,8 @@ isOtherTempNamespace(Oid namespaceId)
  * given database.  The result may be out of date quickly, so the caller
  * must be careful how to handle this information.
  */
-bool
-isTempNamespaceInUse(Oid namespaceId)
+TempNamespaceStatus
+checkTempNamespaceStatus(Oid namespaceId)
 {
 	PGPROC	   *proc;
 	int			backendId;
@@ -3235,25 +3235,25 @@ isTempNamespaceInUse(Oid namespaceId)
 
 	backendId = GetTempNamespaceBackendId(namespaceId);
 
-	/* No such temporary namespace? */
+	/* No such namespace, or its name shows it's not temp? */
 	if (backendId == InvalidBackendId)
-		return false;
+		return TEMP_NAMESPACE_NOT_TEMP;
 
 	/* Is the backend alive? */
 	proc = BackendIdGetProc(backendId);
 	if (proc == NULL)
-		return false;
+		return TEMP_NAMESPACE_IDLE;
 
 	/* Is the backend connected to the same database we are looking at? */
 	if (proc->databaseId != MyDatabaseId)
-		return false;
+		return TEMP_NAMESPACE_IDLE;
 
 	/* Does the backend own the temporary namespace? */
 	if (proc->tempNamespaceId != namespaceId)
-		return false;
+		return TEMP_NAMESPACE_IDLE;
 
-	/* all good to go */
-	return true;
+	/* Yup, so namespace is busy */
+	return TEMP_NAMESPACE_IN_USE;
 }
 
 /*
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 6d1f28c327..e3a43d3296 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2071,9 +2071,10 @@ do_autovacuum(void)
 		{
 			/*
 			 * We just ignore it if the owning backend is still active and
-			 * using the temporary schema.
+			 * using the temporary schema.  Also, for safety, ignore it if the
+			 * namespace doesn't exist or isn't a temp namespace after all.
 			 */
-			if (!isTempNamespaceInUse(classForm->relnamespace))
+			if (checkTempNamespaceStatus(classForm->relnamespace) == TEMP_NAMESPACE_IDLE)
 			{
 				/*
 				 * The table seems to be orphaned -- although it might be that
@@ -2243,7 +2244,7 @@ do_autovacuum(void)
 			continue;
 		}
 
-		if (isTempNamespaceInUse(classForm->relnamespace))
+		if (checkTempNamespaceStatus(classForm->relnamespace) != TEMP_NAMESPACE_IDLE)
 		{
 			UnlockRelationOid(relid, AccessExclusiveLock);
 			continue;
diff --git a/src/include/catalog/namespace.h b/src/include/catalog/namespace.h
index d67f93ae3b..3e3a192471 100644
--- a/src/include/catalog/namespace.h
+++ b/src/include/catalog/namespace.h
@@ -37,6 +37,16 @@ typedef struct _FuncCandidateList
 	Oid			args[FLEXIBLE_ARRAY_MEMBER];	/* arg types */
 }		   *FuncCandidateList;
 
+/*
+ * Result of checkTempNamespaceStatus
+ */
+typedef enum TempNamespaceStatus
+{
+	TEMP_NAMESPACE_NOT_TEMP,	/* nonexistent, or non-temp namespace */
+	TEMP_NAMESPACE_IDLE,		/* exists, belongs to no active session */
+	TEMP_NAMESPACE_IN_USE		/* belongs to some active session */
+} TempNamespaceStatus;
+
 /*
  *	Structure for xxxOverrideSearchPath functions
  */
@@ -138,7 +148,7 @@ extern bool isTempToastNamespace(Oid namespaceId);
 extern bool isTempOrTempToastNamespace(Oid namespaceId);
 extern bool isAnyTempNamespace(Oid namespaceId);
 extern bool isOtherTempNamespace(Oid namespaceId);
-extern bool isTempNamespaceInUse(Oid namespaceId);
+extern TempNamespaceStatus checkTempNamespaceStatus(Oid namespaceId);
 extern int	GetTempNamespaceBackendId(Oid namespaceId);
 extern Oid	GetTempToastNamespace(void);
 extern void GetTempNamespaceState(Oid *tempNamespaceId,