diff --git a/lib/functions.js b/lib/functions.js
index 8186161a..e906ac38 100644
--- a/lib/functions.js
+++ b/lib/functions.js
@@ -14,7 +14,7 @@ var getFunctionCallCreator = function(name, sql) {
 };
 
 // creates a hash of functions for a sql instance
-var getFunctions = function(functionNames, sql) {
+var _getFunctions = function(functionNames, sql) {
   var functions = _.reduce(functionNames, function(reducer, name) {
     reducer[name] = getFunctionCallCreator(name, sql);
     return reducer;
@@ -52,9 +52,18 @@ var hstoreFunction = 'HSTORE';
 
 var standardFunctionNames = aggregateFunctions.concat(scalarFunctions).concat(hstoreFunction);
 
-// creates a hash of standard functions for a sql instance
 var getStandardFunctions = function(sql) {
-  return getFunctions(standardFunctionNames, sql);
+  return _getFunctions(standardFunctionNames, sql);
+}
+
+var getFunctions = function(sql, functionNames) {
+  var functions = _getFunctions(standardFunctionNames, sql);
+  if (functionNames !== undefined) {
+    var customFunctions = _getFunctions(functionNames, sql); 
+    return _.merge(functions, customFunctions);
+  }
+  return functions;
 };
 
+module.exports.getFunctions = getFunctions;
 module.exports.getStandardFunctions = getStandardFunctions;
diff --git a/lib/index.js b/lib/index.js
index 75d1c2e7..adf90011 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -60,6 +60,15 @@ Sql.prototype.setDialect = function(dialect) {
   return this;
 };
 
+Sql.prototype.registerFunctions = function(_functions) {
+  if ( ! _functions instanceof Array) {
+    _functions = [_functions];
+  }
+  // attach the standard SQL functions to this instance
+  this.functions = functions.getFunctions(this, _functions);
+  return this
+}
+
 // back compat shim for the Sql class constructor
 var create = function(dialect) {
   return new Sql(dialect);