diff --git a/src/frontend/Ast.ml b/src/frontend/Ast.ml
index b1ed952251..d0dbfb617c 100644
--- a/src/frontend/Ast.ml
+++ b/src/frontend/Ast.ml
@@ -296,7 +296,9 @@ let rec id_of_lvalue {lval; _} =
         token before the current statement and all the whitespace between two statements
         appears as if it were part of the second statement.
         get_first_loc tries to skip the leading whitespace and approximate the location
-        of the first token in the statement. *)
+        of the first token in the statement.
+    TODO: See if $sloc works better than $loc for this
+*)
 
 let rec get_loc_expr (e : untyped_expression) =
   match e.expr with
diff --git a/src/frontend/Input_warnings.ml b/src/frontend/Input_warnings.ml
index 24549667f8..ebeb65c9c5 100644
--- a/src/frontend/Input_warnings.ml
+++ b/src/frontend/Input_warnings.ml
@@ -19,3 +19,19 @@ let deprecated token (pos, message) =
     Middle.Location_span.of_positions_opt begin_pos end_pos
     |> Option.value ~default:Middle.Location_span.empty in
   add_warning span message
+
+let drop_array_future () =
+  match !warnings with
+  | ( _
+    , "Variable name 'array' will be a reserved word starting in Stan 2.32.0. \
+       Please rename it!" )
+    :: tl ->
+      warnings := tl
+  | _ -> ()
+
+let future_keyword kwrd version (pos1, pos2) =
+  add_warning
+    (Option.value ~default:Middle.Location_span.empty
+       (Middle.Location_span.of_positions_opt pos1 pos2) )
+    ( "Variable name '" ^ kwrd ^ "' will be a reserved word starting in Stan "
+    ^ version ^ ". Please rename it!" )
diff --git a/src/frontend/Input_warnings.mli b/src/frontend/Input_warnings.mli
index b11857c392..a198b629ce 100644
--- a/src/frontend/Input_warnings.mli
+++ b/src/frontend/Input_warnings.mli
@@ -17,3 +17,12 @@ val deprecated : string -> Lexing.position * string -> unit
 
 val empty : string -> unit
 (** Register that an empty file is being lexxed *)
+
+val future_keyword :
+  string -> string -> Lexing.position * Lexing.position -> unit
+(** Warn on a keyword which will be reserved in the future*)
+
+val drop_array_future : unit -> unit
+(** Hack: Remove the most recent warning about array as a future keyword.
+    Needed due to the {e other} hack of how we currently parse arrays.
+*)
diff --git a/src/frontend/parser.mly b/src/frontend/parser.mly
index d4fce160ae..23dd7bd9aa 100644
--- a/src/frontend/parser.mly
+++ b/src/frontend/parser.mly
@@ -21,6 +21,11 @@ let rec iterate_n f x = function
   | n -> iterate_n f (f x) (n - 1)
 let nest_unsized_array basic_type n =
   iterate_n (fun t -> UnsizedType.UArray t) basic_type n
+
+(* $sloc and $symbolstartpos generates code using !=, which
+    Core_kernel considers to be an error.
+ *)
+let (!=) = Stdlib.(!=)
 %}
 
 %token FUNCTIONBLOCK DATABLOCK TRANSFORMEDDATABLOCK PARAMETERSBLOCK
@@ -93,7 +98,7 @@ program:
       let () =
         match (ofb, odb, otdb, opb, otpb, omb, ogb) with
         | None, None, None, None, None, None, None ->
-            Input_warnings.empty (fst $loc).pos_fname
+            Input_warnings.empty ($startpos).pos_fname
         | _ -> ()
       in
       { functionblock= ofb
@@ -160,11 +165,19 @@ generated_quantities_block:
 identifier:
   | id=IDENTIFIER { build_id id $loc }
   | TRUNCATE { build_id "T" $loc}
-  | OFFSET { build_id "offset" $loc}
-  | MULTIPLIER { build_id "multiplier" $loc}
-  | LOWER { build_id "lower" $loc}
-  | UPPER { build_id "upper" $loc}
-  | ARRAY { build_id "array" $loc}
+  | id_and_v = future_keyword
+    {
+      let id, v = id_and_v in
+      Input_warnings.future_keyword id.name v $loc;
+      id
+    }
+
+future_keyword:
+  | OFFSET { build_id "offset" $loc, "2.32.0" }
+  | MULTIPLIER { build_id "multiplier" $loc, "2.32.0" }
+  | LOWER { build_id "lower" $loc, "2.32.0" }
+  | UPPER { build_id "upper" $loc, "2.32.0" }
+  | ARRAY { build_id "array" $loc, "2.32.0" }
 
 decl_identifier:
   | id=identifier { id }
@@ -342,6 +355,7 @@ decl(type_rule, rhs):
       in
       let dims = match dims_opt with
         | Some ({expr= Indexed ({expr= Variable {name="array"; _}; _}, ixs); _}) ->
+            Input_warnings.drop_array_future () ;
            (match int_ixs ixs with
             | Some sizes -> sizes
             | None -> error "Dimensions should be expressions, not multiple or range indexing.")
@@ -358,27 +372,7 @@ decl(type_rule, rhs):
                 ; is_global
                 }
           ; smeta= {
-              loc=
-                (* From the docs:
-                We remark that, if the current production has an empty right-hand side,
-                then $startpos and $endpos are equal, and (by convention) are the end
-                position of the most recently parsed symbol (that is, the symbol that
-                happens to be on top of the automaton’s stack when this production is
-                reduced). If the current production has a nonempty right-hand side,
-                then $startpos is the same as $startpos($1) and $endpos is the same
-                as $endpos($n), where n is the length of the right-hand side.
-
-
-                So when dims_opt is empty, it uses the preview token as its startpos,
-                but that makes the whole declaration think it starts at the previous
-                token. Sadly, $sloc and $symbolstartpos generates code using !=, which
-                Core_kernel considers to be an error.
-                 *)
-                let startpos = match dims_opt with
-                  | None -> $startpos(ty)
-                  | Some _ -> $startpos
-                in
-                Location_span.of_positions_exn (startpos, $endpos)
+              loc= Location_span.of_positions_exn $sloc
             }
           })
     )}
diff --git a/test/integration/bad/lang/stanc.expected b/test/integration/bad/lang/stanc.expected
index fd55ade1df..324bfb20ed 100644
--- a/test/integration/bad/lang/stanc.expected
+++ b/test/integration/bad/lang/stanc.expected
@@ -630,6 +630,8 @@ Syntax error in 'incomplete.stan', line 2, column 18 to column 19, parsing error
 
 Found an incomplete binary expression - are you missing the right hand side?
   $ ../../../../../install/default/bin/stanc incomplete2.stan
+Warning in 'incomplete2.stan', line 2, column 9: Variable name 'upper' will
+    be a reserved word starting in Stan 2.32.0. Please rename it!
 Syntax error in 'incomplete2.stan', line 2, column 17 to column 22, parsing error:
    -------------------------------------------------
      1:  transformed data {
@@ -679,6 +681,8 @@ Syntax error in 'incomplete5.stan', line 3, column 0 to column 0, parsing error:
 
 Ill-formed block. Expected a statement, variable declaration, or just "}".
   $ ../../../../../install/default/bin/stanc incomplete6.stan
+Warning in 'incomplete6.stan', line 2, column 8: Variable name 'upper' will
+    be a reserved word starting in Stan 2.32.0. Please rename it!
 Syntax error in 'incomplete6.stan', line 3, column 16 to column 21, parsing error:
    -------------------------------------------------
      1:  transformed data {
diff --git a/test/integration/bad/new/stanc.expected b/test/integration/bad/new/stanc.expected
index a1ff7a582a..7ec7342b20 100644
--- a/test/integration/bad/new/stanc.expected
+++ b/test/integration/bad/new/stanc.expected
@@ -1198,6 +1198,9 @@ Syntax error in 'ill-formed-statement23.stan', line 1, column 35 to column 39, p
 
 Ill-formed statement. Expected statement after "else".
   $ ../../../../../install/default/bin/stanc ill-formed-statement24.stan
+Warning in 'ill-formed-statement24.stan', line 1, column 30: Variable name
+    'upper' will be a reserved word starting in Stan 2.32.0. Please rename
+    it!
 Syntax error in 'ill-formed-statement24.stan', line 1, column 35 to column 36, parsing error:
    -------------------------------------------------
      1:  transformed data { if ( 1 ) ; upper}
@@ -1214,6 +1217,9 @@ Syntax error in 'ill-formed-statement25.stan', line 1, column 34 to column 38, p
 
 Ill-formed statement. Expected statement after else.
   $ ../../../../../install/default/bin/stanc ill-formed-statement26.stan
+Warning in 'ill-formed-statement26.stan', line 1, column 29: Variable name
+    'upper' will be a reserved word starting in Stan 2.32.0. Please rename
+    it!
 Syntax error in 'ill-formed-statement26.stan', line 1, column 34 to column 34, parsing error:
    -------------------------------------------------
      1:  transformed data { if ( T) ; upper
diff --git a/test/integration/good/pretty.expected b/test/integration/good/pretty.expected
index 4ed973431b..aa1bf602b3 100644
--- a/test/integration/good/pretty.expected
+++ b/test/integration/good/pretty.expected
@@ -3023,6 +3023,11 @@ Warning in 'deprecated_syntax.stan', line 40, column 2: increment_log_prob(...);
 Warning in 'deprecated_syntax.stan', line 42, column 11: get_lp() function is
     deprecated. It will be removed in Stan 2.32.0. Use target() instead. This
     can be done automatically with stanc --print-canonical
+Warning in 'deprecated_syntax.stan', line 46, column 6: Variable name
+    'offset' will be a reserved word starting in Stan 2.32.0. Please rename
+    it!
+Warning in 'deprecated_syntax.stan', line 47, column 6: Variable name 'array'
+    will be a reserved word starting in Stan 2.32.0. Please rename it!
 Warning in 'deprecated_syntax.stan', line 51, column 2: Comments beginning
     with # are deprecated and this syntax will be removed in Stan 2.32.0. Use
     // to begin line comments; this can be done automatically using stanc
@@ -3942,6 +3947,14 @@ data {
   int offset;
 }
 
+Warning in 'identifiers.stan', line 2, column 6: Variable name 'upper' will
+    be a reserved word starting in Stan 2.32.0. Please rename it!
+Warning in 'identifiers.stan', line 3, column 6: Variable name 'lower' will
+    be a reserved word starting in Stan 2.32.0. Please rename it!
+Warning in 'identifiers.stan', line 4, column 6: Variable name 'multiplier'
+    will be a reserved word starting in Stan 2.32.0. Please rename it!
+Warning in 'identifiers.stan', line 5, column 6: Variable name 'offset' will
+    be a reserved word starting in Stan 2.32.0. Please rename it!
   $ ../../../../install/default/bin/stanc --auto-format if-else-formatting.stan
 generated quantities {
   // make sure pp_recursive_ifthenelse properly places else
@@ -6289,6 +6302,15 @@ model {
   array[1, 2, 3] real abc;
 }
 
+Warning in 'unreserved-array-keyword.stan', line 2, column 24: Variable name
+    'array' will be a reserved word starting in Stan 2.32.0. Please rename
+    it!
+Warning in 'unreserved-array-keyword.stan', line 2, column 40: Variable name
+    'array' will be a reserved word starting in Stan 2.32.0. Please rename
+    it!
+Warning in 'unreserved-array-keyword.stan', line 6, column 7: Variable name
+    'array' will be a reserved word starting in Stan 2.32.0. Please rename
+    it!
   $ ../../../../install/default/bin/stanc --auto-format user-defined-lpdf-fun.stan
 functions {
   real bar_lpmf(int y, real z) {