diff --git a/src/passes/1-parser/cameligo/dune b/src/passes/1-parser/cameligo/dune
index 4e6829f1e..8824fdcd4 100644
--- a/src/passes/1-parser/cameligo/dune
+++ b/src/passes/1-parser/cameligo/dune
@@ -7,7 +7,7 @@
 (menhir
   (merge_into Parser)
   (modules ParToken Parser)
-  (flags --table --strict --external-tokens LexToken))
+  (flags -la 1 --table --strict --explain --external-tokens LexToken))
 
 ;; Build of the parser as a library
 
diff --git a/src/passes/1-parser/pascaligo/dune b/src/passes/1-parser/pascaligo/dune
index e7b9a9a73..d0d43f02f 100644
--- a/src/passes/1-parser/pascaligo/dune
+++ b/src/passes/1-parser/pascaligo/dune
@@ -7,7 +7,7 @@
 (menhir
   (merge_into Parser)
   (modules ParToken Parser)
-  (flags --table --strict --external-tokens LexToken))
+  (flags -la 1 --table --strict --explain --external-tokens LexToken))
 
 ;; Build of the parser as a library
 
diff --git a/src/passes/1-parser/reasonligo/dune b/src/passes/1-parser/reasonligo/dune
index a1408af91..6eb7304b8 100644
--- a/src/passes/1-parser/reasonligo/dune
+++ b/src/passes/1-parser/reasonligo/dune
@@ -7,7 +7,7 @@
 (menhir
   (merge_into Parser)
   (modules ParToken Parser)
-  (flags --table --strict --external-tokens LexToken))
+  (flags -la 1 --table --strict --explain --external-tokens LexToken))
 
 ;; Build of the parser as a library
 
diff --git a/vendors/Preproc/build.sh b/vendors/Preproc/build.sh
index 30e3ba705..e9d6546be 100755
--- a/vendors/Preproc/build.sh
+++ b/vendors/Preproc/build.sh
@@ -2,7 +2,7 @@
 set -x
 ocamllex.opt Escan.mll
 ocamllex.opt Preproc.mll
-menhir Eparser.mly
+menhir -la 1 Eparser.mly
 ocamlfind ocamlopt -strict-sequence -w +A-48-4 -c Etree.ml
 ocamlfind ocamlopt -strict-sequence -w +A-48-4 -c Error.ml
 ocamlfind ocamlopt -strict-sequence -w +A-48-4 -c Etree.ml