diff --git a/src/ol/expression/expressions.js b/src/ol/expression/expressions.js
index e51ca718ba..98a608ca2c 100644
--- a/src/ol/expression/expressions.js
+++ b/src/ol/expression/expressions.js
@@ -29,8 +29,9 @@ ol.expression.Expression = function() {};
 /**
  * Evaluate the expression and return the result.
  *
- * @param {Object} scope Evaluation scope.  All properties of this object
- *     will be available as variables when evaluating the expression.
+ * @param {Object=} opt_scope Evaluation scope.  All properties of this object
+ *     will be available as variables when evaluating the expression.  If not
+ *     provided, `null` will be used.
  * @param {Object=} opt_fns Optional scope for looking up functions.  If not
  *     provided, functions will be looked in the evaluation scope.
  * @param {Object=} opt_this Object to use as this when evaluating call
@@ -71,8 +72,8 @@ goog.inherits(ol.expression.Call, ol.expression.Expression);
 /**
  * @inheritDoc
  */
-ol.expression.Call.prototype.evaluate = function(scope, opt_fns, opt_this) {
-  var fnScope = goog.isDefAndNotNull(opt_fns) ? opt_fns : scope;
+ol.expression.Call.prototype.evaluate = function(opt_scope, opt_fns, opt_this) {
+  var fnScope = goog.isDefAndNotNull(opt_fns) ? opt_fns : opt_scope;
   var fn = this.expr_.evaluate(fnScope);
   if (!fn || !goog.isFunction(fn)) {
     throw new Error('Expected function but found ' + fn);
@@ -82,7 +83,7 @@ ol.expression.Call.prototype.evaluate = function(scope, opt_fns, opt_this) {
   var len = this.args_.length;
   var values = new Array(len);
   for (var i = 0; i < len; ++i) {
-    values[i] = this.args_[i].evaluate(scope, opt_fns, opt_this);
+    values[i] = this.args_[i].evaluate(opt_scope, opt_fns, opt_this);
   }
   return fn.apply(thisArg, values);
 };
@@ -156,11 +157,11 @@ ol.expression.Comparison.isValidOp = (function() {
 /**
  * @inheritDoc
  */
-ol.expression.Comparison.prototype.evaluate = function(scope, opt_this,
+ol.expression.Comparison.prototype.evaluate = function(opt_scope, opt_this,
     opt_fns) {
   var result;
-  var rightVal = this.right_.evaluate(scope, opt_fns, opt_this);
-  var leftVal = this.left_.evaluate(scope, opt_fns, opt_this);
+  var rightVal = this.right_.evaluate(opt_scope, opt_fns, opt_this);
+  var leftVal = this.left_.evaluate(opt_scope, opt_fns, opt_this);
 
   switch (this.operator_) {
     case ol.expression.ComparisonOp.EQ:
@@ -217,8 +218,11 @@ goog.inherits(ol.expression.Identifier, ol.expression.Expression);
 /**
  * @inheritDoc
  */
-ol.expression.Identifier.prototype.evaluate = function(scope) {
-  return scope[this.name_];
+ol.expression.Identifier.prototype.evaluate = function(opt_scope) {
+  if (!goog.isDefAndNotNull(opt_scope)) {
+    throw new Error('Attempt to evaluate identifier with no scope');
+  }
+  return opt_scope[this.name_];
 };
 
 
@@ -312,10 +316,11 @@ ol.expression.Logical.isValidOp = (function() {
 /**
  * @inheritDoc
  */
-ol.expression.Logical.prototype.evaluate = function(scope, opt_fns, opt_this) {
+ol.expression.Logical.prototype.evaluate = function(opt_scope, opt_fns,
+    opt_this) {
   var result;
-  var rightVal = this.right_.evaluate(scope, opt_fns, opt_this);
-  var leftVal = this.left_.evaluate(scope, opt_fns, opt_this);
+  var rightVal = this.right_.evaluate(opt_scope, opt_fns, opt_this);
+  var leftVal = this.left_.evaluate(opt_scope, opt_fns, opt_this);
 
   if (this.operator_ === ol.expression.LogicalOp.AND) {
     result = leftVal && rightVal;
@@ -393,10 +398,10 @@ ol.expression.Math.isValidOp = (function() {
 /**
  * @inheritDoc
  */
-ol.expression.Math.prototype.evaluate = function(scope, opt_fns, opt_this) {
+ol.expression.Math.prototype.evaluate = function(opt_scope, opt_fns, opt_this) {
   var result;
-  var rightVal = this.right_.evaluate(scope, opt_fns, opt_this);
-  var leftVal = this.left_.evaluate(scope, opt_fns, opt_this);
+  var rightVal = this.right_.evaluate(opt_scope, opt_fns, opt_this);
+  var leftVal = this.left_.evaluate(opt_scope, opt_fns, opt_this);
   /**
    * TODO: throw if rightVal, leftVal not numbers - this would require the use
    * of a concat function for strings but it would let us serialize these as
@@ -457,8 +462,9 @@ goog.inherits(ol.expression.Member, ol.expression.Expression);
 /**
  * @inheritDoc
  */
-ol.expression.Member.prototype.evaluate = function(scope, opt_fns, opt_this) {
-  var obj = this.expr_.evaluate(scope, opt_fns, opt_this);
+ol.expression.Member.prototype.evaluate = function(opt_scope, opt_fns,
+    opt_this) {
+  var obj = this.expr_.evaluate(opt_scope, opt_fns, opt_this);
   if (!goog.isObject(obj)) {
     throw new Error('Expected member expression to evaluate to an object ' +
         'but got ' + obj);
@@ -490,6 +496,6 @@ goog.inherits(ol.expression.Not, ol.expression.Expression);
 /**
  * @inheritDoc
  */
-ol.expression.Not.prototype.evaluate = function(scope, opt_fns, opt_this) {
-  return !this.expr_.evaluate(scope, opt_fns, opt_this);
+ol.expression.Not.prototype.evaluate = function(opt_scope, opt_fns, opt_this) {
+  return !this.expr_.evaluate(opt_scope, opt_fns, opt_this);
 };
diff --git a/test/spec/ol/expression/expression.test.js b/test/spec/ol/expression/expression.test.js
index dab53c249a..e1ef1d59c1 100644
--- a/test/spec/ol/expression/expression.test.js
+++ b/test/spec/ol/expression/expression.test.js
@@ -26,7 +26,7 @@ describe('ol.expression.parse', function() {
     it('parses string literal expressions', function() {
       var expr = ol.expression.parse('"foo"');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be('foo');
+      expect(expr.evaluate()).to.be('foo');
     });
 
     it('throws on unterminated string', function() {
@@ -38,7 +38,7 @@ describe('ol.expression.parse', function() {
     it('parses numeric literal expressions', function() {
       var expr = ol.expression.parse('.42e+2');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be(42);
+      expect(expr.evaluate()).to.be(42);
     });
 
     it('throws on invalid number', function() {
@@ -50,13 +50,13 @@ describe('ol.expression.parse', function() {
     it('parses boolean literal expressions', function() {
       var expr = ol.expression.parse('false');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be(false);
+      expect(expr.evaluate()).to.be(false);
     });
 
     it('parses null literal expressions', function() {
       var expr = ol.expression.parse('null');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be(null);
+      expect(expr.evaluate()).to.be(null);
     });
 
   });
diff --git a/test/spec/ol/expression/expressions.test.js b/test/spec/ol/expression/expressions.test.js
index 0484895525..1e924fd8e7 100644
--- a/test/spec/ol/expression/expressions.test.js
+++ b/test/spec/ol/expression/expressions.test.js
@@ -250,22 +250,22 @@ describe('ol.expression.Literal', function() {
   describe('#evaluate()', function() {
     it('works for numeric literal', function() {
       var expr = new ol.expression.Literal(42e-11);
-      expect(expr.evaluate({})).to.be(4.2e-10);
+      expect(expr.evaluate()).to.be(4.2e-10);
     });
 
     it('works for string literal', function() {
       var expr = new ol.expression.Literal('asdf');
-      expect(expr.evaluate({})).to.be('asdf');
+      expect(expr.evaluate()).to.be('asdf');
     });
 
     it('works for boolean literal', function() {
       var expr = new ol.expression.Literal(true);
-      expect(expr.evaluate({})).to.be(true);
+      expect(expr.evaluate()).to.be(true);
     });
 
     it('works for null literal', function() {
       var expr = new ol.expression.Literal(null);
-      expect(expr.evaluate({})).to.be(null);
+      expect(expr.evaluate()).to.be(null);
     });
   });
 });
@@ -344,7 +344,7 @@ describe('ol.expression.Math', function() {
           new ol.expression.Literal(40),
           new ol.expression.Literal(2));
 
-      expect(expr.evaluate({})).to.be(42);
+      expect(expr.evaluate()).to.be(42);
     });
 
     it('does + with string literal (note: subject to change)', function() {
@@ -353,7 +353,7 @@ describe('ol.expression.Math', function() {
           new ol.expression.Literal('foo'),
           new ol.expression.Literal('bar'));
 
-      expect(expr.evaluate({})).to.be('foobar');
+      expect(expr.evaluate()).to.be('foobar');
     });
 
     it('does + with identifiers', function() {
@@ -480,30 +480,30 @@ describe('ol.expression.Not', function() {
   describe('#evaluate()', function() {
     it('returns the logical complement', function() {
       var expr = new ol.expression.Not(new ol.expression.Literal(true));
-      expect(expr.evaluate({})).to.be(false);
+      expect(expr.evaluate()).to.be(false);
 
       expr = new ol.expression.Not(new ol.expression.Literal(false));
-      expect(expr.evaluate({})).to.be(true);
+      expect(expr.evaluate()).to.be(true);
     });
 
     it('negates a truthy string', function() {
       var expr = new ol.expression.Not(new ol.expression.Literal('asdf'));
-      expect(expr.evaluate({})).to.be(false);
+      expect(expr.evaluate()).to.be(false);
     });
 
     it('negates a falsy string', function() {
       var expr = new ol.expression.Not(new ol.expression.Literal(''));
-      expect(expr.evaluate({})).to.be(true);
+      expect(expr.evaluate()).to.be(true);
     });
 
     it('negates a truthy number', function() {
       var expr = new ol.expression.Not(new ol.expression.Literal(42));
-      expect(expr.evaluate({})).to.be(false);
+      expect(expr.evaluate()).to.be(false);
     });
 
     it('negates a falsy number', function() {
       var expr = new ol.expression.Not(new ol.expression.Literal(NaN));
-      expect(expr.evaluate({})).to.be(true);
+      expect(expr.evaluate()).to.be(true);
     });
   });
 
diff --git a/test/spec/ol/expression/parser.test.js b/test/spec/ol/expression/parser.test.js
index 4d7e478b5e..1ff0e8c9cd 100644
--- a/test/spec/ol/expression/parser.test.js
+++ b/test/spec/ol/expression/parser.test.js
@@ -36,25 +36,25 @@ describe('ol.expression.Parser', function() {
     it('parses string literal', function() {
       var expr = parse('"foo"');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be('foo');
+      expect(expr.evaluate()).to.be('foo');
     });
 
     it('parses numeric literal', function() {
       var expr = parse('.42e2');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be(42);
+      expect(expr.evaluate()).to.be(42);
     });
 
     it('parses boolean literal', function() {
       var expr = parse('.42e2');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be(42);
+      expect(expr.evaluate()).to.be(42);
     });
 
     it('parses null literal', function() {
       var expr = parse('null');
       expect(expr).to.be.a(ol.expression.Literal);
-      expect(expr.evaluate({})).to.be(null);
+      expect(expr.evaluate()).to.be(null);
     });
 
   });