diff --git a/src/backend/access/gist/gistbuildbuffers.c b/src/backend/access/gist/gistbuildbuffers.c
index 4f2363e..1d008ec 100644
--- a/src/backend/access/gist/gistbuildbuffers.c
+++ b/src/backend/access/gist/gistbuildbuffers.c
@@ -17,6 +17,7 @@
 #include "access/genam.h"
 #include "access/gist_private.h"
 #include "catalog/index.h"
+#include "commands/tablespace.h"
 #include "miscadmin.h"
 #include "storage/buffile.h"
 #include "storage/bufmgr.h"
@@ -58,6 +59,8 @@ gistInitBuildBuffers(int pagesPerBuffer, int levelStep, int maxLevel)
 	 * Create a temporary file to hold buffer pages that are swapped out of
 	 * memory.
 	 */
+	PrepareTempTablespaces();
+
 	gfbb->pfile = BufFileCreateTemp(false);
 	gfbb->nFileBlocks = 0;
 
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index fdac985..a4463ba 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -1459,6 +1459,9 @@ PathNameDeleteTemporaryDir(const char *dirname)
  * outlive the transaction that created them, so this should be false -- but
  * if you need "somewhat" temporary storage, this might be useful. In either
  * case, the file is removed when the File is explicitly closed.
+ *
+ * Unless interXact is true, some caller function should have done
+ * PrepareTempTablespaces().
  */
 File
 OpenTemporaryFile(bool interXact)
@@ -1481,7 +1484,7 @@ OpenTemporaryFile(bool interXact)
 	 * force it into the database's default tablespace, so that it will not
 	 * pose a threat to possible tablespace drop attempts.
 	 */
-	if (numTempTableSpaces > 0 && !interXact)
+	if (!interXact)
 	{
 		Oid			tblspcOid = GetNextTempTableSpace();
 
@@ -2732,6 +2735,7 @@ GetTempTablespaces(Oid *tableSpaces, int numSpaces)
 Oid
 GetNextTempTableSpace(void)
 {
+	Assert(TempTablespacesAreSet());
 	if (numTempTableSpaces > 0)
 	{
 		/* Advance nextTempTableSpace counter with wraparound */