diff --git a/src/jbuild.ml b/src/jbuild.ml
index 7b460de3..9a2c780d 100644
--- a/src/jbuild.ml
+++ b/src/jbuild.ml
@@ -1129,7 +1129,9 @@ module Rule = struct
     field "deps"    (list Dep_conf.t) ~default:[] >>= fun deps ->
     field "locks"   (list String_with_vars.t) ~default:[] >>= fun locks ->
     map_validate
-      (field_b "fallback" >>= fun fallback ->
+      (field_b
+         ~check:(Syntax.renamed_in Stanza.syntax (1, 0) ~to_:"(mode fallback)")
+         "fallback" >>= fun fallback ->
        field_o "mode" Mode.t >>= fun mode ->
        return (fallback, mode))
       ~f:(function
diff --git a/src/stdune/sexp.ml b/src/stdune/sexp.ml
index 4ef365ff..e98d1886 100644
--- a/src/stdune/sexp.ml
+++ b/src/stdune/sexp.ml
@@ -481,9 +481,10 @@ module Of_sexp = struct
     | None ->
       (None, add_known name state)
 
-  let field_b name =
+  let field_b ?check name =
     field name ~default:false
-      (eos >>= function
+      (Option.value check ~default:(return ()) >>= fun () ->
+        eos >>= function
        | true -> return true
        | _ -> bool)
 
diff --git a/src/stdune/sexp.mli b/src/stdune/sexp.mli
index f1f62e3b..6c147db1 100644
--- a/src/stdune/sexp.mli
+++ b/src/stdune/sexp.mli
@@ -216,7 +216,7 @@ module Of_sexp : sig
     -> 'a t
     -> 'a option fields_parser
 
-  val field_b : string -> bool fields_parser
+  val field_b : ?check:(unit t) -> string -> bool fields_parser
 
   (** A field that can appear multiple times *)
   val multi_field
diff --git a/src/syntax.ml b/src/syntax.ml
index dae362fa..8a95138c 100644
--- a/src/syntax.ml
+++ b/src/syntax.ml
@@ -124,7 +124,7 @@ let renamed_in t ver ~to_ =
   else begin
     desc () >>= fun (loc, what) ->
     Loc.fail loc
-      "%s was renamed to '%s' in %s of %s" what to_
+      "%s was renamed to '%s' in the %s version of %s" what to_
       (Version.to_string ver) t.desc
   end
 
diff --git a/test/blackbox-tests/dune.inc b/test/blackbox-tests/dune.inc
index 28390f9e..efcea69d 100644
--- a/test/blackbox-tests/dune.inc
+++ b/test/blackbox-tests/dune.inc
@@ -128,6 +128,14 @@
    test-cases/exec-cmd
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name fallback-dune)
+ (deps (package dune) (source_tree test-cases/fallback-dune))
+ (action
+  (chdir
+   test-cases/fallback-dune
+   (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
+
 (alias
  (name findlib)
  (deps (package dune) (source_tree test-cases/findlib))
@@ -606,6 +614,7 @@
   (alias env)
   (alias exclude-missing-module)
   (alias exec-cmd)
+  (alias fallback-dune)
   (alias findlib)
   (alias findlib-error)
   (alias force-test)
@@ -678,6 +687,7 @@
   (alias env)
   (alias exclude-missing-module)
   (alias exec-cmd)
+  (alias fallback-dune)
   (alias findlib)
   (alias findlib-error)
   (alias force-test)
diff --git a/test/blackbox-tests/test-cases/fallback-dune/dune1/dune b/test/blackbox-tests/test-cases/fallback-dune/dune1/dune
new file mode 100644
index 00000000..020ea118
--- /dev/null
+++ b/test/blackbox-tests/test-cases/fallback-dune/dune1/dune
@@ -0,0 +1,4 @@
+(rule
+ (fallback)
+ (targets) 
+ (action (with-stdout-to foo.txt (echo "testing"))))
\ No newline at end of file
diff --git a/test/blackbox-tests/test-cases/fallback-dune/dune2/dune b/test/blackbox-tests/test-cases/fallback-dune/dune2/dune
new file mode 100644
index 00000000..fdf0a419
--- /dev/null
+++ b/test/blackbox-tests/test-cases/fallback-dune/dune2/dune
@@ -0,0 +1,4 @@
+(rule
+ (fallback false)
+ (targets) 
+ (action (with-stdout-to foo.txt (echo "testing"))))
\ No newline at end of file
diff --git a/test/blackbox-tests/test-cases/fallback-dune/jbuild/jbuild b/test/blackbox-tests/test-cases/fallback-dune/jbuild/jbuild
new file mode 100644
index 00000000..9792612a
--- /dev/null
+++ b/test/blackbox-tests/test-cases/fallback-dune/jbuild/jbuild
@@ -0,0 +1,5 @@
+
+(rule
+ ((fallback)
+  (targets (foo.txt))
+  (action (with-stdout-to foo.txt (echo "testing")))))
diff --git a/test/blackbox-tests/test-cases/fallback-dune/run.t b/test/blackbox-tests/test-cases/fallback-dune/run.t
new file mode 100644
index 00000000..d2580573
--- /dev/null
+++ b/test/blackbox-tests/test-cases/fallback-dune/run.t
@@ -0,0 +1,20 @@
+fallback isn't allowed in dune
+
+  $ dune build --root dune1
+  Info: creating file dune-project with this contents: (lang dune 1.0)
+  File "dune", line 2, characters 1-11:
+  Error: 'fallback' was renamed to '(mode fallback)' in the 1.0 version of the dune language
+  [1]
+
+2nd fallback form isn't allowed either
+
+  $ dune build --root dune2
+  Info: creating file dune-project with this contents: (lang dune 1.0)
+  File "dune", line 2, characters 1-17:
+  Error: 'fallback' was renamed to '(mode fallback)' in the 1.0 version of the dune language
+  [1]
+
+But it is allowed in jbuilder
+
+  $ jbuilder build --root jbuild
+  Entering directory 'jbuild'