diff --git a/lib/conditionals.js b/lib/conditionals.js
index 165d588b6..ed96ac495 100644
--- a/lib/conditionals.js
+++ b/lib/conditionals.js
@@ -34,10 +34,12 @@
  *
  *   These conditions can also be negated via:
  *     
- *     import 'es5-shim#?~./conditions.js|es6'
+ *     import 'es5-shim#?./conditions.js|~es6'
  *
  */
 
+  var sysConditions = ['browser', 'node', 'dev', 'production', 'default'];
+
   function parseCondition(condition) {
     var conditionExport, conditionModule, negation;
 
@@ -45,11 +47,23 @@
     var conditionExportIndex = condition.lastIndexOf('|');
     if (conditionExportIndex != -1) {
       conditionExport = condition.substr(conditionExportIndex + 1);
-      conditionModule = condition.substr(negation, conditionExportIndex - negation) || '@system-env';
+      conditionModule = condition.substr(negation, conditionExportIndex - negation);
+      
+      if (negation)
+        warn.call(this, 'Condition negation form "' + condition + '" is deprecated for "' + conditionModule + '|~' + conditionExport + '"');
+
+      if (conditionExport[0] == '~') {
+        negation = true;
+        conditionExport = conditionExport.substr(1);
+      }
     }
     else {
       conditionExport = null;
       conditionModule = condition.substr(negation);
+      if (sysConditions.indexOf(conditionModule) != -1) {
+        conditionExport = conditionModule;
+        conditionModule = '@system-env';
+      }
     }
 
     return {
@@ -60,7 +74,7 @@
   }
 
   function serializeCondition(conditionObj) {
-    return (conditionObj.negate ? '~' : '') + conditionObj.module + (conditionObj.prop ? '|' + conditionObj.prop : '');
+    return conditionObj.module + (conditionObj.prop ? '|' + conditionObj.prop : '');
   }
 
   function resolveCondition(conditionObj, parentName, bool) {
@@ -86,7 +100,7 @@
     if (!conditionalMatch)
       return Promise.resolve(name);
 
-    var conditionObj = parseCondition(conditionalMatch[0].substr(2, conditionalMatch[0].length - 3));
+    var conditionObj = parseCondition.call(this, conditionalMatch[0].substr(2, conditionalMatch[0].length - 3));
 
     // in builds, return normalized conditional
     if (this.builder)
@@ -115,7 +129,7 @@
     if (booleanIndex == -1)
       return Promise.resolve(name);
 
-    var conditionObj = parseCondition(name.substr(booleanIndex + 2));
+    var conditionObj = parseCondition.call(this, name.substr(booleanIndex + 2));
 
     // in builds, return normalized conditional
     if (this.builder)
diff --git a/lib/core.js b/lib/core.js
index 005664423..5996c720a 100644
--- a/lib/core.js
+++ b/lib/core.js
@@ -293,7 +293,7 @@ hook('instantiate', function(instantiate) {
   For easy normalization canonicalization with latest URL support.
 
 */
-SystemJSLoader.prototype.env = 'development';
+SystemJSLoader.prototype.env = 'dev';
 
 var curCurScript;
 SystemJSLoader.prototype.config = function(cfg, isEnvConfig) {
@@ -314,8 +314,8 @@ SystemJSLoader.prototype.config = function(cfg, isEnvConfig) {
   if (cfg.transpilerRuntime === false)
     loader._loader.loadedTranspilerRuntime = true;
 
-  if (cfg.production)
-    setProduction.call(loader, true);
+  if ('production' in cfg)
+    setProduction.call(loader, cfg.production);
 
   if (!isEnvConfig) {
     // if using nodeConfig / browserConfig / productionConfig, take baseURL from there
diff --git a/lib/package.js b/lib/package.js
index 5e3498fb8..02669f3a9 100644
--- a/lib/package.js
+++ b/lib/package.js
@@ -26,7 +26,8 @@
  *
  *        // environment-specific map configurations
  *        './index.js': {
- *          '~browser': './index-node.js'
+ *          '~browser': './index-node.js',
+ *          './custom-condition.js|~export': './index-custom.js'
  *        }
  *     },
  *     // allows for setting package-prefixed depCache
@@ -284,17 +285,27 @@
     if (loader.builder)
       return Promise.resolve(pkgName + '/#:' + path);
 
+    // we load all conditions upfront
+    var conditionPromises = [];
+    var conditions = [];
+    for (var e in mapped) {
+      var c = parseCondition(e);
+      conditions.push({
+        condition: c,
+        map: mapped[e]
+      });
+      conditionPromises.push(loader['import'](c.module, pkgName));
+    }
+
     // map object -> conditional map
-    return loader['import'](pkg.map['@env'] || '@system-env', pkgName)
-    .then(function(env) {
+    return Promise.all(conditionPromises)
+    .then(function(conditionValues) {
       // first map condition to match is used
-      for (var e in mapped) {
-        var negate = e[0] == '~';
-
-        var value = readMemberExpression(negate ? e.substr(1) : e, env);
-
-        if (!negate && value || negate && !value)
-          return mapped[e];
+      for (var i = 0; i < conditions.length; i++) {
+        var c = conditions[i].condition;
+        var value = readMemberExpression(c.prop, conditionValues[i]);
+        if (!c.negate && value || c.negate && !value)
+          return conditions[i].map;
       }
     })
     .then(function(mapped) {