diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 5006a5c464..e85c75e0e6 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -566,11 +566,13 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
 {
 	Snapshot	snap;
 	TransactionId xid;
+	TransactionId safeXid;
 	TransactionId *newxip;
 	int			newxcnt = 0;
 
 	Assert(!FirstSnapshotSet);
 	Assert(XactIsoLevel == XACT_REPEATABLE_READ);
+	Assert(builder->building_full_snapshot);
 
 	if (builder->state != SNAPBUILD_CONSISTENT)
 		elog(ERROR, "cannot build an initial slot snapshot before reaching a consistent state");
@@ -589,17 +591,13 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
 	 * mechanism. Due to that we can do this without locks, we're only
 	 * changing our own value.
 	 */
-#ifdef USE_ASSERT_CHECKING
-	{
-		TransactionId safeXid;
-
-		LWLockAcquire(ProcArrayLock, LW_SHARED);
-		safeXid = GetOldestSafeDecodingTransactionId(false);
-		LWLockRelease(ProcArrayLock);
+	LWLockAcquire(ProcArrayLock, LW_SHARED);
+	safeXid = GetOldestSafeDecodingTransactionId(false);
+	LWLockRelease(ProcArrayLock);
 
-		Assert(TransactionIdPrecedesOrEquals(safeXid, snap->xmin));
-	}
-#endif
+	if (TransactionIdFollows(safeXid, snap->xmin))
+		elog(ERROR, "cannot build an initial slot snapshot when oldest safe xid %u follows snapshot's xmin %u",
+			 safeXid, snap->xmin);
 
 	MyProc->xmin = snap->xmin;