diff --git a/common/mltools/JSON.ml b/common/mltools/JSON.ml
index 1a88f8b1f..a51037ab4 100644
--- a/common/mltools/JSON.ml
+++ b/common/mltools/JSON.ml
@@ -23,6 +23,7 @@ and json_t =
   | String of string
   | Int of int
   | Int64 of int64
+  | Float of float
   | Bool of bool
   | List of json_t list
   | Dict of field list
@@ -110,6 +111,11 @@ and output_field ~indent ~fmt = function
   | Int i -> string_of_int i
   | Bool b -> if b then "true" else "false"
   | Int64 i -> Int64.to_string i
+  (* The JSON standard permits either "1" or "1.0" but not "1.".
+   * OCaml string_of_float will generate "1.", but the %g formatter
+   * will only generate the valid JSON values.
+   *)
+  | Float f -> Printf.sprintf "%g" f
   | List l -> output_list ~indent:(indent + 1) ~fmt l
   | Dict d -> output_dict ~indent:(indent + 1) ~fmt d
 
diff --git a/common/mltools/JSON.mli b/common/mltools/JSON.mli
index 5b487af8e..06a777c20 100644
--- a/common/mltools/JSON.mli
+++ b/common/mltools/JSON.mli
@@ -23,6 +23,7 @@ and json_t =                    (** JSON value. *)
   | String of string            (** string value, eg. ["string"] *)
   | Int of int                  (** int value, eg. [99] *)
   | Int64 of int64              (** int64 value, eg. [99] *)
+  | Float of float              (** floating point value, eg. [9.9] *)
   | Bool of bool                (** boolean value, [true] or [false] *)
   | List of json_t list         (** array value, eg. [[1,2,3]] *)
   | Dict of field list          (** object, eg. [{ "a": 1, "b": "c" }] *)
diff --git a/common/mltools/JSON_tests.ml b/common/mltools/JSON_tests.ml
index 55a474474..2f3998e6e 100644
--- a/common/mltools/JSON_tests.ml
+++ b/common/mltools/JSON_tests.ml
@@ -71,6 +71,25 @@ let test_int ctx =
 }"
     (JSON.string_of_doc ~fmt:JSON.Indented doc)
 
+let test_float ctx =
+  let doc = [ "test_zero", JSON.Float 0.;
+              "test_one", JSON.Float 1.;
+              "test_frac", JSON.Float 1.5;
+              "test_neg_frac", JSON.Float (-1.5);
+              "test_exp", JSON.Float 1e100 ] in
+  assert_equal_string
+    "{ \"test_zero\": 0, \"test_one\": 1, \"test_frac\": 1.5, \"test_neg_frac\": -1.5, \"test_exp\": 1e+100 }"
+    (JSON.string_of_doc doc);
+  assert_equal_string
+    "{
+  \"test_zero\": 0,
+  \"test_one\": 1,
+  \"test_frac\": 1.5,
+  \"test_neg_frac\": -1.5,
+  \"test_exp\": 1e+100
+}"
+    (JSON.string_of_doc ~fmt:JSON.Indented doc)
+
 let test_list ctx =
   let doc = [ "item", JSON.List [ JSON.String "foo"; JSON.Int 10; JSON.Bool true ] ] in
   assert_equal_string
@@ -227,6 +246,7 @@ let suite =
       "basic.string" >:: test_string;
       "basic.bool" >:: test_bool;
       "basic.int" >:: test_int;
+      "basic.float" >:: test_float;
       "basic.list" >:: test_list;
       "basic.nested_dict" >:: test_nested_dict;
       "basic.nested_nested dict" >:: test_nested_nested_dict;