diff --git a/LOG b/LOG
index 78ea6ab0cc..7e775314b5 100644
--- a/LOG
+++ b/LOG
@@ -937,3 +937,5 @@
     wininstall/product.wxs
 - Use Windows path separator character when finding boot files on Windows.
     scheme.c
+- Propagate enable-check-prelex-flags to separate-eval sub-process in tests.
+    mats.ss
\ No newline at end of file
diff --git a/mats/mat.ss b/mats/mat.ss
index 4a4e5477b7..f82e406c73 100644
--- a/mats/mat.ss
+++ b/mats/mat.ss
@@ -380,6 +380,7 @@
                   (open-process-ports (format "~a -q" (patch-exec-path *scheme*))
                     (buffer-mode block)
                     (native-transcoder))])
+      (pretty-print `(#%$enable-check-prelex-flags ,(#%$enable-check-prelex-flags)) to-stdin)
       (for-each (lambda (expr) (pretty-print expr to-stdin)) expr*)
       (close-port to-stdin)
       (let* ([stdout-stuff (slurp from-stdout)]