diff --git a/benchmark/prepare-values.js b/benchmark/prepare-values.js
new file mode 100644
index 000000000..49e973e7a
--- /dev/null
+++ b/benchmark/prepare-values.js
@@ -0,0 +1,46 @@
+var utils = require("../lib/utils");
+
+var numArr = [];
+for (var i = 0; i < 1000; i++) numArr[i] = i;
+console.time("prepare-number-array");
+for (var i = 0; i < 100; i++) {
+  utils.prepareValue(numArr);
+}
+console.timeEnd("prepare-number-array");
+
+
+var strArr = new Array(10000);
+console.time("prepare-string-array");
+for (var i = 0; i < 100; i++) {
+  utils.prepareValue(strArr);
+}
+console.timeEnd("prepare-string-array");
+
+
+var objArr = [];
+for (var i = 0; i < 1000; i++) objArr[i] = { x: { y: 42 }};
+console.time("prepare-object-array");
+for (var i = 0; i < 100; i++) {
+  utils.prepareValue(objArr);
+}
+console.timeEnd("prepare-object-array");
+
+
+var obj = { x: { y: 42 }};
+console.time("prepare-object");
+for (var i = 0; i < 100000; i++) {
+  utils.prepareValue(obj);
+}
+console.timeEnd("prepare-object");
+
+
+var customType = {
+  toPostgres: function () {
+    return { toPostgres: function () { return new Date(); } };
+  }
+};
+console.time("prepare-custom-type");
+for (var i = 0; i < 100000; i++) {
+  utils.prepareValue(customType);
+}
+console.timeEnd("prepare-custom-type");
diff --git a/lib/utils.js b/lib/utils.js
index fb1f56ebe..2c20a77da 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -17,53 +17,62 @@ if(typeof events.EventEmitter.prototype.once !== 'function') {
 // uses comma separator so won't work for types like box that use
 // a different array separator.
 function arrayString(val) {
-	var result = '{';
-	for (var i = 0 ; i < val.length; i++) {
-		if(i > 0) {
-			result = result + ',';
-		}
-		if(val[i] instanceof Date) {
-			result = result + JSON.stringify(val[i]);
-		}
-		else if(typeof val[i] === 'undefined') {
-			result = result + 'NULL';
-		}
-		else if(Array.isArray(val[i])) {
-			result = result + arrayString(val[i]);
-		}
-		else
-		{
-			result = result +
-				(val[i] === null ? 'NULL' : JSON.stringify(val[i]));
-		}
-	}
-	result = result + '}';
-	return result;
+  var result = '{';
+  for (var i = 0 ; i < val.length; i++) {
+    if(i > 0) {
+      result = result + ',';
+    }
+    if(val[i] === null || typeof val[i] === 'undefined') {
+      result = result + 'NULL';
+    }
+    else if(Array.isArray(val[i])) {
+      result = result + arrayString(val[i]);
+    }
+    else
+    {
+      result = result + JSON.stringify(prepareValue(val[i]));
+    }
+  }
+  result = result + '}';
+  return result;
 }
 
 //converts values from javascript types
 //to their 'raw' counterparts for use as a postgres parameter
 //note: you can override this function to provide your own conversion mechanism
 //for complex types, etc...
-var prepareValue = function(val) {
+var prepareValue = function(val, seen) {
   if (val instanceof Buffer) {
     return val;
   }
   if(val instanceof Date) {
     return dateToString(val);
   }
-  if(typeof val === 'undefined') {
-    return null;
-  }
   if(Array.isArray(val)) {
     return arrayString(val);
   }
-  if(!val || typeof val !== 'object') {
-    return val === null ? null : val.toString();
+  if(val === null || typeof val === 'undefined') {
+    return null;
+  }
+  if(typeof val === 'object') {
+    return prepareObject(val, seen);
   }
-  return JSON.stringify(val);
+  return val.toString();
 };
 
+function prepareObject(val, seen) {
+  if(val.toPostgres && typeof val.toPostgres === 'function') {
+    seen = seen || [];
+    if (seen.indexOf(val) !== -1) {
+      throw new Error('circular reference detected while preparing "' + val + '" for query');
+    }
+    seen.push(val);
+
+    return prepareValue(val.toPostgres(prepareValue), seen);
+  }
+  return JSON.stringify(val);
+}
+
 function dateToString(date) {
   function pad(number, digits) {
     number = ""+number;
diff --git a/test/test-helper.js b/test/test-helper.js
index 8d854b819..757b200b4 100644
--- a/test/test-helper.js
+++ b/test/test-helper.js
@@ -222,6 +222,15 @@ var Sink = function(expected, timeout, callback) {
   }
 }
 
+var getTimezoneOffset = Date.prototype.getTimezoneOffset;
+
+var setTimezoneOffset = function(minutesOffset) {
+  Date.prototype.getTimezoneOffset = function () { return minutesOffset; };
+}
+
+var resetTimezoneOffset = function() {
+  Date.prototype.getTimezoneOffset = getTimezoneOffset;
+}
 
 module.exports = {
   Sink: Sink,
@@ -229,7 +238,9 @@ module.exports = {
   args: args,
   config: args,
   sys: sys,
-  Client: Client
+  Client: Client,
+  setTimezoneOffset: setTimezoneOffset,
+  resetTimezoneOffset: resetTimezoneOffset
 };
 
 
diff --git a/test/unit/utils-tests.js b/test/unit/utils-tests.js
index 56c81dc52..116dfdd1e 100644
--- a/test/unit/utils-tests.js
+++ b/test/unit/utils-tests.js
@@ -1,4 +1,4 @@
-require(__dirname + '/test-helper');
+var helper = require(__dirname + '/test-helper');
 var utils = require(__dirname + "/../../lib/utils");
 var defaults = require(__dirname + "/../../lib").defaults;
 
@@ -48,3 +48,126 @@ test('normalizing query configs', function() {
   config = utils.normalizeQueryConfig({text: 'TEXT', values: [10]}, callback)
   assert.deepEqual(config, {text: 'TEXT', values: [10], callback: callback})
 })
+
+test('prepareValues: buffer prepared properly', function() {
+  var buf = new Buffer("quack");
+  var out = utils.prepareValue(buf);
+  assert.strictEqual(buf, out);
+});
+
+test('prepareValues: date prepared properly', function() {
+  helper.setTimezoneOffset(-330);
+
+  var date = new Date(2014, 1, 1, 11, 11, 1, 7);
+  var out = utils.prepareValue(date);
+  assert.strictEqual(out, "2014-02-01T11:11:01.007+05:30");
+
+  helper.resetTimezoneOffset();
+});
+
+test('prepareValues: undefined prepared properly', function() {
+  var out = utils.prepareValue(void 0);
+  assert.strictEqual(out, null);
+});
+
+test('prepareValue: null prepared properly', function() {
+  var out = utils.prepareValue(null);
+  assert.strictEqual(out, null);
+});
+
+test('prepareValue: true prepared properly', function() {
+  var out = utils.prepareValue(true);
+  assert.strictEqual(out, 'true');
+});
+
+test('prepareValue: false prepared properly', function() {
+  var out = utils.prepareValue(false);
+  assert.strictEqual(out, 'false');
+});
+
+test('prepareValue: number prepared properly', function () {
+  var out = utils.prepareValue(3.042);
+  assert.strictEqual(out, '3.042');
+});
+
+test('prepareValue: string prepared properly', function() {
+  var out = utils.prepareValue('big bad wolf');
+  assert.strictEqual(out, 'big bad wolf');
+});
+
+test('prepareValue: simple array prepared properly', function() {
+  var out = utils.prepareValue([1, null, 3, undefined, [5, 6, "squ,awk"]]);
+  assert.strictEqual(out, '{"1",NULL,"3",NULL,{"5","6","squ,awk"}}');
+});
+
+test('prepareValue: complex array prepared properly', function() {
+  var out = utils.prepareValue([{ x: 42 }, { y: 84 }]);
+  assert.strictEqual(out, '{"{\\"x\\":42}","{\\"y\\":84}"}');
+});
+
+test('prepareValue: date array prepared properly', function() {
+  helper.setTimezoneOffset(-330);
+
+  var date = new Date(2014, 1, 1, 11, 11, 1, 7);
+  var out = utils.prepareValue([date]);
+  assert.strictEqual(out, '{"2014-02-01T11:11:01.007+05:30"}');
+
+  helper.resetTimezoneOffset();
+});
+
+test('prepareValue: arbitrary objects prepared properly', function() {
+  var out = utils.prepareValue({ x: 42 });
+  assert.strictEqual(out, '{"x":42}');
+});
+
+test('prepareValue: objects with simple toPostgres prepared properly', function() {
+  var customType = {
+    toPostgres: function() {
+      return "zomgcustom!";
+    }
+  };
+  var out = utils.prepareValue(customType);
+  assert.strictEqual(out, "zomgcustom!");
+});
+
+test('prepareValue: objects with complex toPostgres prepared properly', function() {
+  var buf = new Buffer("zomgcustom!");
+  var customType = {
+    toPostgres: function() {
+      return [1, 2];
+    }
+  };
+  var out = utils.prepareValue(customType);
+  assert.strictEqual(out, '{"1","2"}');
+});
+
+test('prepareValue: objects with toPostgres receive prepareValue', function() {
+  var customRange = {
+    lower: { toPostgres: function() { return 5; } },
+    upper: { toPostgres: function() { return 10; } },
+    toPostgres: function(prepare) {
+      return "[" + prepare(this.lower) + "," + prepare(this.upper) + "]";
+    }
+  };
+  var out = utils.prepareValue(customRange);
+  assert.strictEqual(out, "[5,10]");
+});
+
+test('prepareValue: objects with circular toPostgres rejected', function() {
+  var buf = new Buffer("zomgcustom!");
+  var customType = {
+    toPostgres: function() {
+      return { toPostgres: function () { return customType; } };
+    }
+  };
+
+  //can't use `assert.throws` since we need to distinguish circular reference
+  //errors from call stack exceeded errors
+  try {
+    utils.prepareValue(customType);
+  } catch (e) {
+    assert.ok(e.message.match(/circular/), "Expected circular reference error but got " + e);
+    return;
+  }
+  throw new Error("Expected prepareValue to throw exception");
+});