diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 94fbf1aa19..5dac9f0696 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -1594,14 +1594,14 @@ LookupOpclassInfo(Oid operatorClassOid,
 		/* First time through: initialize the opclass cache */
 		HASHCTL		ctl;
 
+		/* Also make sure CacheMemoryContext exists */
+		if (!CacheMemoryContext)
+			CreateCacheMemoryContext();
+
 		ctl.keysize = sizeof(Oid);
 		ctl.entrysize = sizeof(OpClassCacheEnt);
 		OpClassCache = hash_create("Operator class cache", 64,
 								   &ctl, HASH_ELEM | HASH_BLOBS);
-
-		/* Also make sure CacheMemoryContext exists */
-		if (!CacheMemoryContext)
-			CreateCacheMemoryContext();
 	}
 
 	opcentry = (OpClassCacheEnt *) hash_search(OpClassCache,
@@ -1610,16 +1610,10 @@ LookupOpclassInfo(Oid operatorClassOid,
 
 	if (!found)
 	{
-		/* Need to allocate memory for new entry */
+		/* Initialize new entry */
 		opcentry->valid = false;	/* until known OK */
 		opcentry->numSupport = numSupport;
-
-		if (numSupport > 0)
-			opcentry->supportProcs = (RegProcedure *)
-				MemoryContextAllocZero(CacheMemoryContext,
-									   (numSupport + 1) * sizeof(RegProcedure));
-		else
-			opcentry->supportProcs = NULL;
+		opcentry->supportProcs = NULL;	/* filled below */
 	}
 	else
 	{
@@ -1627,14 +1621,17 @@ LookupOpclassInfo(Oid operatorClassOid,
 	}
 
 	/*
-	 * When testing for cache-flush hazards, we intentionally disable the
-	 * operator class cache and force reloading of the info on each call. This
-	 * is helpful because we want to test the case where a cache flush occurs
-	 * while we are loading the info, and it's very hard to provoke that if
-	 * this happens only once per opclass per backend.
+	 * When aggressively testing cache-flush hazards, we disable the operator
+	 * class cache and force reloading of the info on each call.  This models
+	 * no real-world behavior, since the cache entries are never invalidated
+	 * otherwise.  However it can be helpful for detecting bugs in the cache
+	 * loading logic itself, such as reliance on a non-nailed index.  Given
+	 * the limited use-case and the fact that this adds a great deal of
+	 * expense, we enable it only for high values of
+	 * debug_invalidate_system_caches_always.
 	 */
 #ifdef CLOBBER_CACHE_ENABLED
-	if (debug_invalidate_system_caches_always > 0)
+	if (debug_invalidate_system_caches_always > 2)
 		opcentry->valid = false;
 #endif
 
@@ -1642,8 +1639,15 @@ LookupOpclassInfo(Oid operatorClassOid,
 		return opcentry;
 
 	/*
-	 * Need to fill in new entry.
-	 *
+	 * Need to fill in new entry.  First allocate space, unless we already did
+	 * so in some previous attempt.
+	 */
+	if (opcentry->supportProcs == NULL && numSupport > 0)
+		opcentry->supportProcs = (RegProcedure *)
+			MemoryContextAllocZero(CacheMemoryContext,
+								   numSupport * sizeof(RegProcedure));
+
+	/*
 	 * To avoid infinite recursion during startup, force heap scans if we're
 	 * looking up info for the opclasses used by the indexes we would like to
 	 * reference here.