From 6c06a9f295a72a64acf828d3f66c7dc196c8a818 Mon Sep 17 00:00:00 2001
From: krangelov <kr.angelov@gmail.com>
Date: Tue, 31 Aug 2021 20:02:49 +0200
Subject: [PATCH] readExpr needs an additional call to mask_

---
 src/runtime/haskell/PGF2.hsc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/runtime/haskell/PGF2.hsc b/src/runtime/haskell/PGF2.hsc
index ca36c4d84..b49520333 100644
--- a/src/runtime/haskell/PGF2.hsc
+++ b/src/runtime/haskell/PGF2.hsc
@@ -280,7 +280,8 @@ readExpr :: String -> Maybe Expr
 readExpr str =
   unsafePerformIO $
   withText str $ \c_str ->
-  withForeignPtr unmarshaller $ \u -> do
+  withForeignPtr unmarshaller $ \u ->
+  mask_ $ do
     c_expr <- pgf_read_expr c_str u
     if c_expr == castPtrToStablePtr nullPtr
       then return Nothing