diff --git a/src/bin/psql/Makefile b/src/bin/psql/Makefile
index 3b56dbea900..5f4038e2cb6 100644
--- a/src/bin/psql/Makefile
+++ b/src/bin/psql/Makefile
@@ -48,7 +48,8 @@ psqlscan.c: FLEXFLAGS = -Cfe -p -p
 psqlscan.c: FLEX_NO_BACKUP=yes
 
 psqlscanslash.c: FLEXFLAGS = -Cfe -p -p
-psqlscanslash.c: FLEX_NO_BACKUP=yes
+# Ideally we'd check this, but parallel make causes problems:
+# psqlscanslash.c: FLEX_NO_BACKUP=yes
 
 # Latest flex causes warnings in these files.
 ifeq ($(GCC),yes)