diff --git a/src/evalvars.c b/src/evalvars.c
index 9dbdc75..7578378 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -443,15 +443,26 @@
     char_u	*difffile,
     char_u	*outfile)
 {
-    int		err;
+    sctx_T	saved_sctx = current_sctx;
+    sctx_T	*ctx;
+    typval_T	*tv;
 
     set_vim_var_string(VV_FNAME_IN, origfile, -1);
     set_vim_var_string(VV_FNAME_DIFF, difffile, -1);
     set_vim_var_string(VV_FNAME_OUT, outfile, -1);
-    (void)eval_to_bool(p_pex, &err, NULL, FALSE);
+
+    ctx = get_option_sctx("patchexpr");
+    if (ctx != NULL)
+	current_sctx = *ctx;
+
+    // errors are ignored
+    tv = eval_expr(p_pex, NULL);
+    free_tv(tv);
+
     set_vim_var_string(VV_FNAME_IN, NULL, -1);
     set_vim_var_string(VV_FNAME_DIFF, NULL, -1);
     set_vim_var_string(VV_FNAME_OUT, NULL, -1);
+    current_sctx = saved_sctx;
 }
 # endif