diff --git a/package.json b/package.json
index 890c64f..59cbafa 100644
--- a/package.json
+++ b/package.json
@@ -34,7 +34,7 @@
   },
   "sideEffects": false,
   "dependencies": {
-    "d3-array": "^2.3.0",
+    "d3-array": "^2.12.0",
     "d3-format": "1 - 2",
     "d3-interpolate": "1.2.0 - 2",
     "d3-time": "1 - 2",
diff --git a/src/ordinal.js b/src/ordinal.js
index e98f600..f4513c5 100644
--- a/src/ordinal.js
+++ b/src/ordinal.js
@@ -1,29 +1,28 @@
 import {initRange} from "./init.js";
+import {InternMap} from "d3-array";
 
 export const implicit = Symbol("implicit");
 
 export default function ordinal() {
-  var index = new Map(),
+  var index = new InternMap(),
       domain = [],
       range = [],
       unknown = implicit;
 
   function scale(d) {
-    var key = d + "", i = index.get(key);
-    if (!i) {
+    if (!index.has(d)) {
       if (unknown !== implicit) return unknown;
-      index.set(key, i = domain.push(d));
+      index.set(d, domain.push(d));
     }
-    return range[(i - 1) % range.length];
+    return range[(index.get(d) - 1) % range.length];
   }
 
   scale.domain = function(_) {
     if (!arguments.length) return domain.slice();
-    domain = [], index = new Map();
+    domain = [], index = new InternMap();
     for (const value of _) {
-      const key = value + "";
-      if (index.has(key)) continue;
-      index.set(key, domain.push(value));
+      if (index.has(value)) continue;
+      index.set(value, domain.push(value));
     }
     return scale;
   };
diff --git a/test/ordinal-test.js b/test/ordinal-test.js
index b8b10ff..b72d887 100644
--- a/test/ordinal-test.js
+++ b/test/ordinal-test.js
@@ -87,6 +87,29 @@ tape("ordinal.domain() does not coerce domain values to strings", function(test)
   test.end();
 });
 
+tape("ordinal() accepts dates", function(test) {
+  var s = scale.scaleOrdinal();
+  s(new Date(1970, 2, 1));
+  s(new Date(2001, 4, 13));
+  s(new Date(1970, 2, 1));
+  s(new Date(2001, 4, 13));
+  test.deepEqual(s.domain(), [new Date(1970, 2, 1), new Date(2001, 4, 13)]);
+  test.end();
+});
+
+tape("ordinal.domain() accepts dates", function(test) {
+  var s = scale.scaleOrdinal().domain([
+    new Date(1970, 2, 1),
+    new Date(2001, 4, 13),
+    new Date(1970, 2, 1),
+    new Date(2001, 4, 13)
+  ]);
+  s(new Date(1970, 2, 1));
+  s(new Date(1999, 11, 31));
+  test.deepEqual(s.domain(), [new Date(1970, 2, 1), new Date(2001, 4, 13), new Date(1999, 11, 31)]);
+  test.end();
+});
+
 tape("ordinal.domain() does not barf on object built-ins", function(test) {
   var s = scale.scaleOrdinal().domain(["__proto__", "hasOwnProperty"]).range([42, 43]);
   test.equal(s("__proto__"), 42);
diff --git a/yarn.lock b/yarn.lock
index b6206db..9239b99 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -169,10 +169,12 @@ cross-spawn@^6.0.5:
     shebang-command "^1.2.0"
     which "^1.2.9"
 
-d3-array@^2.3.0:
-  version "2.8.0"
-  resolved "https://registry.yarnpkg.com/d3-array/-/d3-array-2.8.0.tgz#f76e10ad47f1f4f75f33db5fc322eb9ffde5ef23"
-  integrity sha512-6V272gsOeg7+9pTW1jSYOR1QE37g95I3my1hBmY+vOUNHRrk9yt4OTz/gK7PMkVAVDrYYq4mq3grTiZ8iJdNIw==
+d3-array@^2.12.0:
+  version "2.12.0"
+  resolved "https://registry.yarnpkg.com/d3-array/-/d3-array-2.12.0.tgz#68a74d153e52d6bf4608d9f6388cca48b42a4c3f"
+  integrity sha512-T6H/qNldyD/1OlRkJbonb3u3MPhNwju8OPxYv0YSjDb/B2RUeeBEHzIpNrYiinwpmz8+am+puMrpcrDWgY9wRg==
+  dependencies:
+    internmap "^1.0.0"
 
 "d3-color@1 - 2":
   version "2.0.0"
@@ -548,6 +550,11 @@ inquirer@^6.4.1:
     strip-ansi "^5.1.0"
     through "^2.3.6"
 
+internmap@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/internmap/-/internmap-1.0.1.tgz#0017cc8a3b99605f0302f2b198d272e015e5df95"
+  integrity sha512-lDB5YccMydFBtasVtxnZ3MRBHuaoE8GKsppq+EchKL2U4nK/DmEpPHNH8MZe5HkMtpSiTSOZwfN0tzYjO/lJEw==
+
 is-callable@^1.1.3, is-callable@^1.1.4:
   version "1.1.4"
   resolved "https://registry.yarnpkg.com/is-callable/-/is-callable-1.1.4.tgz#1e1adf219e1eeb684d691f9d6a05ff0d30a24d75"