diff --git a/builder/list_entries.ml b/builder/list_entries.ml
index c64d554a2..f1f67290c 100644
--- a/builder/list_entries.ml
+++ b/builder/list_entries.ml
@@ -117,7 +117,7 @@ and list_entries_json ~sources index =
           | None -> item
           | Some str -> ("full-name", JSON.String str) :: item in
         let item = ("arch", JSON.String (Index.string_of_arch arch)) :: item in
-        let item = ("size", JSON.Int64 size) :: item in
+        let item = ("size", JSON.Int size) :: item in
         let item =
           match compressed_size with
           | None -> item
@@ -148,7 +148,7 @@ and list_entries_json ~sources index =
         JSON.Dict (List.rev item)
     ) index in
   let doc = [
-    "version", JSON.Int 1;
+    "version", JSON.Int 1L;
     "sources", JSON.List json_sources;
     "templates", JSON.List json_templates;
   ] in
diff --git a/common/mltools/JSON.ml b/common/mltools/JSON.ml
index a51037ab4..8c2e695e2 100644
--- a/common/mltools/JSON.ml
+++ b/common/mltools/JSON.ml
@@ -21,8 +21,7 @@
 type field = string * json_t
 and json_t =
   | String of string
-  | Int of int
-  | Int64 of int64
+  | Int of int64
   | Float of float
   | Bool of bool
   | List of json_t list
@@ -108,14 +107,13 @@ and output_list fields ~fmt ~indent =
 
 and output_field ~indent ~fmt = function
   | String s -> json_quote_string s
-  | Int i -> string_of_int i
-  | Bool b -> if b then "true" else "false"
-  | Int64 i -> Int64.to_string i
+  | Int 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
+  | Bool b -> if b then "true" else "false"
   | 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 06a777c20..c85b786ff 100644
--- a/common/mltools/JSON.mli
+++ b/common/mltools/JSON.mli
@@ -21,8 +21,7 @@
 type field = string * json_t    (** ["field": "value"] *)
 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] *)
+  | Int of int64                (** int 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]] *)
diff --git a/common/mltools/JSON_tests.ml b/common/mltools/JSON_tests.ml
index 2f3998e6e..6bd98af26 100644
--- a/common/mltools/JSON_tests.ml
+++ b/common/mltools/JSON_tests.ml
@@ -18,6 +18,8 @@
 
 (* This file tests the JSON module. *)
 
+open Std_utils
+
 open OUnit2
 
 (* Utils. *)
@@ -53,21 +55,21 @@ let test_bool ctx =
     (JSON.string_of_doc ~fmt:JSON.Indented doc)
 
 let test_int ctx =
-  let doc = [ "test_zero", JSON.Int 0;
-              "test_pos", JSON.Int 5;
-              "test_neg", JSON.Int (-5);
-              "test_pos64", JSON.Int64 (Int64.of_int 10);
-              "test_neg64", JSON.Int64 (Int64.of_int (-10)); ] in
+  let doc = [ "test_zero", JSON.Int 0L;
+              "test_pos", JSON.Int 5L;
+              "test_neg", JSON.Int (-5L);
+              "test_pos64", JSON.Int 1_000_000_000_000L;
+              "test_neg64", JSON.Int (-1_000_000_000_000L); ] in
   assert_equal_string
-    "{ \"test_zero\": 0, \"test_pos\": 5, \"test_neg\": -5, \"test_pos64\": 10, \"test_neg64\": -10 }"
+    "{ \"test_zero\": 0, \"test_pos\": 5, \"test_neg\": -5, \"test_pos64\": 1000000000000, \"test_neg64\": -1000000000000 }"
     (JSON.string_of_doc doc);
   assert_equal_string
     "{
   \"test_zero\": 0,
   \"test_pos\": 5,
   \"test_neg\": -5,
-  \"test_pos64\": 10,
-  \"test_neg64\": -10
+  \"test_pos64\": 1000000000000,
+  \"test_neg64\": -1000000000000
 }"
     (JSON.string_of_doc ~fmt:JSON.Indented doc)
 
@@ -91,7 +93,7 @@ let test_float ctx =
     (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
+  let doc = [ "item", JSON.List [ JSON.String "foo"; JSON.Int 10L; JSON.Bool true ] ] in
   assert_equal_string
     "{ \"item\": [ \"foo\", 10, true ] }"
     (JSON.string_of_doc doc);
@@ -107,8 +109,8 @@ let test_list ctx =
 
 let test_nested_dict ctx =
   let doc = [
-      "item", JSON.Dict [ "int", JSON.Int 5; "string", JSON.String "foo"; ];
-      "last", JSON.Int 10;
+      "item", JSON.Dict [ "int", JSON.Int 5L; "string", JSON.String "foo"; ];
+      "last", JSON.Int 10L;
     ] in
   assert_equal_string
     "{ \"item\": { \"int\": 5, \"string\": \"foo\" }, \"last\": 10 }"
@@ -125,10 +127,10 @@ let test_nested_dict ctx =
 
 let test_nested_nested_dict ctx =
   let doc = [
-      "item", JSON.Dict [ "int", JSON.Int 5;
-        "item2", JSON.Dict [ "int", JSON.Int 0; ];
+      "item", JSON.Dict [ "int", JSON.Int 5L;
+        "item2", JSON.Dict [ "int", JSON.Int 0L; ];
       ];
-      "last", JSON.Int 10;
+      "last", JSON.Int 10L;
     ] in
   assert_equal_string
     "{ \"item\": { \"int\": 5, \"item2\": { \"int\": 0 } }, \"last\": 10 }"
@@ -159,8 +161,8 @@ let test_qemu ctx =
   let doc = [
     "file.driver", JSON.String "https";
     "file.url", JSON.String "https://libguestfs.org";
-    "file.timeout", JSON.Int 60;
-    "file.readahead", JSON.Int (64 * 1024 * 1024);
+    "file.timeout", JSON.Int 60L;
+    "file.readahead", JSON.Int (64L *^ 1024L *^ 1024L);
   ] in
   assert_equal_string
     "{ \"file.driver\": \"https\", \"file.url\": \"https://libguestfs.org\", \"file.timeout\": 60, \"file.readahead\": 67108864 }"
@@ -176,7 +178,7 @@ let test_qemu ctx =
 
 let test_builder ctx =
   let doc = [
-    "version", JSON.Int 1;
+    "version", JSON.Int 1L;
     "sources", JSON.List [
       JSON.Dict [
         "uri", JSON.String "http://libguestfs.org/index";
@@ -187,7 +189,7 @@ let test_builder ctx =
         "os-version", JSON.String "phony-debian";
         "full-name", JSON.String "Phony Debian";
         "arch", JSON.String "x86_64";
-        "size", JSON.Int64 536870912_L;
+        "size", JSON.Int 536870912_L;
         "notes", JSON.Dict [
           "C", JSON.String "Phony Debian look-alike used for testing.";
         ];
@@ -197,7 +199,7 @@ let test_builder ctx =
         "os-version", JSON.String "phony-fedora";
         "full-name", JSON.String "Phony Fedora";
         "arch", JSON.String "x86_64";
-        "size", JSON.Int64 1073741824_L;
+        "size", JSON.Int 1073741824_L;
         "notes", JSON.Dict [
           "C", JSON.String "Phony Fedora look-alike used for testing.";
         ];
diff --git a/v2v/input_libvirt_xen_ssh.ml b/v2v/input_libvirt_xen_ssh.ml
index 597957f92..c4b671490 100644
--- a/v2v/input_libvirt_xen_ssh.ml
+++ b/v2v/input_libvirt_xen_ssh.ml
@@ -83,7 +83,7 @@ object
           (* qemu will actually assert-fail if you send the port
            * number as a string ...
            *)
-          | i -> ("file.port", JSON.Int i) :: json_params in
+          | i -> ("file.port", JSON.Int (Int64.of_int i)) :: json_params in
 
         let json_params =
           match parsed_uri.uri_user with
diff --git a/v2v/input_ova.ml b/v2v/input_ova.ml
index bfd72dee4..d5c9f1203 100644
--- a/v2v/input_ova.ml
+++ b/v2v/input_ova.ml
@@ -161,8 +161,8 @@ class input_ova ova = object
            let doc = [
                "file", JSON.Dict [
                            "driver", JSON.String "raw";
-                           "offset", JSON.Int64 offset;
-                           "size", JSON.Int64 size;
+                           "offset", JSON.Int offset;
+                           "size", JSON.Int size;
                            "file", JSON.Dict [
                                        "driver", JSON.String "file";
                                        "filename", JSON.String tar_path]
diff --git a/v2v/input_vmx.ml b/v2v/input_vmx.ml
index 4f67630dc..b169b2537 100644
--- a/v2v/input_vmx.ml
+++ b/v2v/input_vmx.ml
@@ -245,7 +245,7 @@ and qemu_uri_of_filename vmx_source filename =
        match port_of_uri uri with
        | None -> json_params
        | Some port ->
-          ("file.port", JSON.Int port) :: json_params in
+          ("file.port", JSON.Int (Int64.of_int port)) :: json_params in
 
      "json:" ^ JSON.string_of_doc json_params, format
 
diff --git a/v2v/output_rhv_upload.ml b/v2v/output_rhv_upload.ml
index 966323cae..f03e1ede3 100644
--- a/v2v/output_rhv_upload.ml
+++ b/v2v/output_rhv_upload.ml
@@ -276,7 +276,7 @@ object
 
         let disk_size = ov.ov_virtual_size in
         let json_params =
-          ("disk_size", JSON.Int64 disk_size) :: json_params in
+          ("disk_size", JSON.Int disk_size) :: json_params in
 
         (* Ask the plugin to write the disk ID to a special file. *)
         let diskid_file = diskid_file_of_id id in
diff --git a/v2v/parse_libvirt_xml.ml b/v2v/parse_libvirt_xml.ml
index dac99511c..255c935a6 100644
--- a/v2v/parse_libvirt_xml.ml
+++ b/v2v/parse_libvirt_xml.ml
@@ -63,8 +63,8 @@ let create_curl_qemu_uri driver host port path =
   let json_params = [
     "file.driver", JSON.String driver;  (* "http" or "https" *)
     "file.url", JSON.String url;
-    "file.timeout", JSON.Int 2000;
-    "file.readahead", JSON.Int (1024 * 1024);
+    "file.timeout", JSON.Int 2000_L;
+    "file.readahead", JSON.Int (1024_L *^ 1024_L);
     (* "file.sslverify", JSON.String "off"; XXX *)
   ] in
 
diff --git a/v2v/utils.ml b/v2v/utils.ml
index 67e2028f3..63ef91c51 100644
--- a/v2v/utils.ml
+++ b/v2v/utils.ml
@@ -114,8 +114,8 @@ let qemu_img_supports_offset_and_size () =
   let json = [
       "file", JSON.Dict [
         "driver", JSON.String "raw";
-        "offset", JSON.Int 512;
-        "size", JSON.Int 512;
+        "offset", JSON.Int 512_L;
+        "size", JSON.Int 512_L;
         "file", JSON.Dict [
           "filename", JSON.String tmp
         ]
diff --git a/v2v/vCenter.ml b/v2v/vCenter.ml
index e97d25ce1..cf124f067 100644
--- a/v2v/vCenter.ml
+++ b/v2v/vCenter.ml
@@ -78,14 +78,14 @@ let rec map_source ?readahead ?password_file dcPath uri server path =
       "file.driver", JSON.String "https";
       "file.url", JSON.String https_url;
       (* https://bugzilla.redhat.com/show_bug.cgi?id=1146007#c10 *)
-      "file.timeout", JSON.Int 2000;
+      "file.timeout", JSON.Int 2000_L;
     ] in
 
     let json_params =
       match readahead with
       | None -> json_params
       | Some readahead ->
-         ("file.readahead", JSON.Int readahead) :: json_params in
+         ("file.readahead", JSON.Int (Int64.of_int readahead)) :: json_params in
 
     let json_params =
       if sslverify then json_params