diff --git a/src/d3-ext/util.js b/src/d3-ext/util.js
new file mode 100644
index 0000000..4f0e010
--- /dev/null
+++ b/src/d3-ext/util.js
@@ -0,0 +1,23 @@
+/**
+ * @fileOverview
+ * Utility functions related to d3 selections.
+ */
+define(
+function() {
+  'use strict';
+
+  return {
+
+    /**
+     * Same as d3.select but allows a d3.selection as input too.
+     * @param {d3.selection|string} selection
+     */
+    select: function(selection) {
+      return (selection instanceof d3.selection) ?
+        selection :
+        d3.select(selection);
+    }
+
+  };
+
+});
diff --git a/test/unit/d3-ext/util.spec.js b/test/unit/d3-ext/util.spec.js
new file mode 100644
index 0000000..b25da7d
--- /dev/null
+++ b/test/unit/d3-ext/util.spec.js
@@ -0,0 +1,32 @@
+define([
+  'd3-ext/util'
+],
+function(selection) {
+  'use strict';
+
+  describe('d3-ext.selection', function() {
+
+    beforeEach(function() {
+    });
+
+    it('selects with a text selector', function() {
+      var fixture = jasmine.htmlFixture(),
+        sel = selection.select('#html-fixture');
+      expect(sel.node()).toBe(fixture.node());
+    });
+
+    it('selects with a d3 selection', function() {
+      var fixture = jasmine.htmlFixture(),
+        sel = selection.select(d3.select('#html-fixture'));
+      expect(sel.node()).toBe(fixture.node());
+    });
+
+    it('selects with an DOM node', function() {
+      var fixture = jasmine.htmlFixture(),
+        sel = selection.select(fixture.node());
+      expect(sel.node()).toBe(fixture.node());
+    });
+
+  });
+
+});