diff --git a/src/com/cognitect/transit/handlers.js b/src/com/cognitect/transit/handlers.js
index a67beb9..9d55690 100644
--- a/src/com/cognitect/transit/handlers.js
+++ b/src/com/cognitect/transit/handlers.js
@@ -124,7 +124,11 @@ goog.scope(function () {
     handlers.NumberHandler = function Transit$NumberHandler() {
     };
     handlers.NumberHandler.prototype.tag = function (v) {
-        return "i";
+        if (isNaN(v) || v === Infinity || v === -Infinity || v % 1 === 0) {
+            return "i";
+        } else {
+            return "d";
+        }
     };
     handlers.NumberHandler.prototype.rep = function (v) {
         return v;
diff --git a/src/com/cognitect/transit/impl/writer.js b/src/com/cognitect/transit/impl/writer.js
index f2ad33a..4daa3ae 100644
--- a/src/com/cognitect/transit/impl/writer.js
+++ b/src/com/cognitect/transit/impl/writer.js
@@ -143,11 +143,11 @@ goog.scope(function () {
         }
     };
 
-    writer.JSONMarshaller.prototype.emitDouble = function (d, asMapKey, cache) {
+    writer.JSONMarshaller.prototype.emitDouble = function (n, asMapKey, cache) {
         if (asMapKey) {
-            return this.emitString(d.ESC, "d", d, asMapKey, cache);
+            return this.emitString(d.ESC, "d", n, asMapKey, cache);
         } else {
-            return d;
+            return n;
         }
     };
 
diff --git a/test/tests.js b/test/tests.js
index 5842f52..1f3e54f 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -1056,6 +1056,26 @@ exports.testWriteSpecialDoubleValues = function(test) {
     test.done();
 };
 
+// =============================================================================
+// Double values as map keys
+// =============================================================================
+
+exports.testReadDoubleValuesAsMapKeys = function(test) {
+    var r = transit.reader();
+
+    test.ok(transit.equals(r.read("[\"^ \",\"~d1.1\",1.1]"), transit.map([1.1, 1.1])));
+
+    test.done();
+};
+
+exports.testWriteDoubleValuesAsMapKeys = function(test) {
+    var w = transit.writer();
+
+    test.equal(w.write(transit.map([1.1, 1.1])), "[\"^ \",\"~d1.1\",1.1]");
+
+    test.done();
+};
+
 // =============================================================================
 // Map Not Found
 // =============================================================================
@@ -1291,7 +1311,7 @@ exports.testBadCache = function(test) {
         w = t.writer("json"),
         r = t.reader("json");
 
-    transit.equals(pathological, r.read(w.write(pathological)));
+    test.ok(transit.equals(pathological, r.read(w.write(pathological))));
 
     test.done();
 };
\ No newline at end of file