diff --git a/release.nix b/release.nix
index 6b571644d9..3f4c487612 100644
--- a/release.nix
+++ b/release.nix
@@ -19,7 +19,7 @@ let
         inherit officialRelease;
 
         buildInputs =
-          [ curl bison24 flex2535 perl libxml2 libxslt w3m bzip2
+          [ curl bison25 flex2535 perl libxml2 libxslt w3m bzip2
             tetex dblatex nukeReferences pkgconfig sqlite git
           ];
 
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 449123a1f8..095e288430 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -8,6 +8,8 @@
 %parse-param { ParseData * data }
 %lex-param { yyscan_t scanner }
 %lex-param { ParseData * data }
+%expect 1
+%expect-rr 1
 
 %code requires {