diff --git a/src/babel/transformation/modules/_default.js b/src/babel/transformation/modules/_default.js
index 5b7ea1ab88..d563e51bb6 100644
--- a/src/babel/transformation/modules/_default.js
+++ b/src/babel/transformation/modules/_default.js
@@ -1,78 +1,16 @@
 import * as messages from "../../messages";
+import Remaps from "./lib/remaps";
 import extend from "lodash/object/extend";
 import object from "../../helpers/object";
 import * as util from  "../../util";
 import * as t from "../../types";
 
-var remapVisitor = {
-  enter(node) {
-    if (node._skipModulesRemap) {
-      return this.skip();
-    }
-  },
-
-  ReferencedIdentifier(node, parent, scope, formatter) {
-    var remap = formatter.internalRemap[node.name];
-
-    if (remap && node !== remap) {
-      if (!scope.hasBinding(node.name) || scope.bindingIdentifierEquals(node.name, formatter.localImports[node.name])) {
-        if (this.key === "callee" && this.parentPath.isCallExpression()) {
-          return t.sequenceExpression([t.literal(0), remap]);
-        } else {
-          return remap;
-        }
-      }
-    }
-  },
-
-  AssignmentExpression: {
-    exit(node, parent, scope, formatter) {
-      if (!node._ignoreModulesRemap) {
-        var exported = formatter.getExport(node.left, scope);
-        if (exported) {
-          return formatter.remapExportAssignment(node, exported);
-        }
-      }
-    }
-  },
-
-  UpdateExpression(node, parent, scope, formatter) {
-    var exported = formatter.getExport(node.argument, scope);
-    if (!exported) return;
-
-    this.skip();
-
-    // expand to long file assignment expression
-    var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
-
-    // remap this assignment expression
-    var remapped = formatter.remapExportAssignment(assign, exported);
-
-    // we don't need to change the result
-    if (t.isExpressionStatement(parent) || node.prefix) {
-      return remapped;
-    }
-
-    var nodes = [];
-    nodes.push(remapped);
-
-    var operator;
-    if (node.operator === "--") {
-      operator = "+";
-    } else { // "++"
-      operator = "-";
-    }
-    nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
-
-    return t.sequenceExpression(nodes);
-  }
-};
-
 var metadataVisitor = {
   ModuleDeclaration: {
     enter(node, parent, scope, formatter) {
       if (node.source) {
         node.source.value = formatter.file.resolveModuleSource(node.source.value);
+        formatter.addScope(this);
       }
     }
   },
@@ -218,18 +156,27 @@ var metadataVisitor = {
     }
   },
 
-  Scope() {
-    this.skip();
+  Scope(node, parent, scope, formatter) {
+    if (!formatter.isLoose()) {
+      this.skip();
+    }
   }
 };
 
 export default class DefaultFormatter {
   constructor(file) {
-    this.internalRemap = object();
-    this.defaultIds    = object();
-    this.scope         = file.scope;
-    this.file          = file;
-    this.ids           = object();
+    // object containg all module sources with the scope that they're contained in
+    this.sourceScopes = object();
+
+    // ids for use in module ids
+    this.defaultIds = object();
+    this.ids        = object();
+
+    // contains reference aliases for live bindings
+    this.remaps = new Remaps(file, this);
+
+    this.scope = file.scope;
+    this.file  = file;
 
     this.hasNonDefaultExports = false;
 
@@ -243,6 +190,18 @@ export default class DefaultFormatter {
     this.getMetadata();
   }
 
+  addScope(path) {
+    var source = path.node.source && path.node.source.value;
+    if (!source) return;
+
+    var existingScope = this.sourceScopes[source];
+    if (existingScope && existingScope !== path.scope) {
+      throw path.errorWithNode(messages.get("modulesDuplicateDeclarations"));
+    }
+
+    this.sourceScopes[source] = path.scope;
+  }
+
   isModuleType(node, type) {
     var modules = this.file.dynamicImportTypes[type];
     return modules && modules.indexOf(node) >= 0;
@@ -264,12 +223,14 @@ export default class DefaultFormatter {
         break;
       }
     }
-    if (has) this.file.path.traverse(metadataVisitor, this);
+    if (has || this.isLoose()) {
+      this.file.path.traverse(metadataVisitor, this);
+    }
   }
 
   remapAssignments() {
     if (this.hasLocalExports || this.hasLocalImports) {
-      this.file.path.traverse(remapVisitor, this);
+      this.remaps.run();
     }
   }
 
diff --git a/src/babel/transformation/modules/amd.js b/src/babel/transformation/modules/amd.js
index c6932d8574..a660373731 100644
--- a/src/babel/transformation/modules/amd.js
+++ b/src/babel/transformation/modules/amd.js
@@ -72,7 +72,7 @@ export default class AMDFormatter extends DefaultFormatter {
     this.getExternalReference(node);
   }
 
-  importSpecifier(specifier, node, nodes) {
+  importSpecifier(specifier, node, nodes, scope) {
     var key = node.source.value;
     var ref = this.getExternalReference(node);
 
@@ -90,7 +90,7 @@ export default class AMDFormatter extends DefaultFormatter {
       // import * as bar from "foo";
     } else if (!includes(this.file.dynamicImported, node) && t.isSpecifierDefault(specifier) && !this.noInteropRequireImport) {
       // import foo from "foo";
-      var uid = this.scope.generateUidIdentifier(specifier.local.name);
+      var uid = scope.generateUidIdentifier(specifier.local.name);
       nodes.push(t.variableDeclaration("var", [
         t.variableDeclarator(uid, t.callExpression(this.file.addHelper("interop-require-default"), [ref]))
       ]));
@@ -102,7 +102,7 @@ export default class AMDFormatter extends DefaultFormatter {
       ref = t.memberExpression(ref, imported);
     }
 
-    this.internalRemap[specifier.local.name] = ref;
+    this.remaps.add(scope, specifier.local.name, ref);
   }
 
   exportSpecifier(specifier, node, nodes) {
diff --git a/src/babel/transformation/modules/common.js b/src/babel/transformation/modules/common.js
index 2fd23d5af1..9293d88b46 100644
--- a/src/babel/transformation/modules/common.js
+++ b/src/babel/transformation/modules/common.js
@@ -37,7 +37,7 @@ export default class CommonJSFormatter extends DefaultFormatter {
     }
   }
 
-  importSpecifier(specifier, node, nodes) {
+  importSpecifier(specifier, node, nodes, scope) {
     var variableName = specifier.local;
 
     var ref = this.getExternalReference(node, nodes);
@@ -47,9 +47,9 @@ export default class CommonJSFormatter extends DefaultFormatter {
       if (this.isModuleType(node, "absolute")) {
         // absolute module reference
       } else if (this.isModuleType(node, "absoluteDefault")) {
-        this.internalRemap[variableName.name] = ref;
+        this.remaps.add(scope, variableName.name, ref);
       } else if (this.noInteropRequireImport) {
-        this.internalRemap[variableName.name] = t.memberExpression(ref, t.identifier("default"));
+        this.remaps.add(scope, variableName.name, t.memberExpression(ref, t.identifier("default")));
       } else {
         var uid = this.scope.generateUidIdentifierBasedOnNode(node, "import");
 
@@ -57,7 +57,7 @@ export default class CommonJSFormatter extends DefaultFormatter {
           t.variableDeclarator(uid, t.callExpression(this.file.addHelper("interop-require-default"), [ref]))
         ]));
 
-        this.internalRemap[variableName.name] = t.memberExpression(uid, t.identifier("default"));
+        this.remaps.add(scope, variableName.name, t.memberExpression(uid, t.identifier("default")));
       }
     } else {
       if (t.isImportNamespaceSpecifier(specifier)) {
@@ -71,7 +71,7 @@ export default class CommonJSFormatter extends DefaultFormatter {
         ]));
       } else {
         // import { foo } from "foo";
-        this.internalRemap[variableName.name] = t.memberExpression(ref, specifier.imported);
+        this.remaps.add(scope, variableName.name, t.memberExpression(ref, specifier.imported));
       }
     }
   }
diff --git a/src/babel/transformation/modules/lib/remaps.js b/src/babel/transformation/modules/lib/remaps.js
new file mode 100644
index 0000000000..a02ffd1766
--- /dev/null
+++ b/src/babel/transformation/modules/lib/remaps.js
@@ -0,0 +1,119 @@
+import * as t from "../../../types";
+
+var remapVisitor = {
+  enter(node) {
+    if (node._skipModulesRemap) {
+      return this.skip();
+    }
+  },
+
+  ReferencedIdentifier(node, parent, scope, remaps) {
+    var remap = remaps.get(scope, node.name);
+    if (!remap || node === remap) return;
+
+    if (!scope.hasBinding(node.name) ||
+        scope.bindingIdentifierEquals(node.name, remaps.formatter.localImports[node.name])) {
+      if (this.key === "callee" && this.parentPath.isCallExpression()) {
+        return t.sequenceExpression([t.literal(0), remap]);
+      } else {
+        return remap;
+      }
+    }
+  },
+
+  AssignmentExpression: {
+    exit(node, parent, scope, { formatter }) {
+      if (!node._ignoreModulesRemap) {
+        var exported = formatter.getExport(node.left, scope);
+        if (exported) {
+          return formatter.remapExportAssignment(node, exported);
+        }
+      }
+    }
+  },
+
+  UpdateExpression(node, parent, scope, { formatter }) {
+    var exported = formatter.getExport(node.argument, scope);
+    if (!exported) return;
+
+    this.skip();
+
+    // expand to long file assignment expression
+    var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
+
+    // remap this assignment expression
+    var remapped = formatter.remapExportAssignment(assign, exported);
+
+    // we don't need to change the result
+    if (t.isExpressionStatement(parent) || node.prefix) {
+      return remapped;
+    }
+
+    var nodes = [];
+    nodes.push(remapped);
+
+    var operator;
+    if (node.operator === "--") {
+      operator = "+";
+    } else { // "++"
+      operator = "-";
+    }
+    nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
+
+    return t.sequenceExpression(nodes);
+  }
+};
+export default class Remaps {
+  constructor(file, formatter) {
+    this.formatter = formatter;
+    this.file      = file;
+  }
+
+  run() {
+    this.file.path.traverse(remapVisitor, this);
+  }
+
+  _getKey(name) {
+    return `${name}:moduleRemap`;
+  }
+
+  get(scope, name) {
+    return scope.getData(this._getKey(name));
+  }
+
+  add(scope, name, val) {
+    if (this.all) {
+      this.all.push({
+        name,
+        scope,
+        node: val
+      });
+    }
+
+    return scope.setData(this._getKey(name), val);
+  }
+
+  remove(scope, name) {
+    return scope.removeData(this._getKey(name));
+  }
+
+  /**
+   * These methods are used by the system module formatter who needs access to all the remaps
+   * so it can process them into it's specific setter method. We don't do this by default since
+   * no other module formatters need access to this.
+   */
+
+  getAll() {
+    return this.all;
+  }
+
+  clearAll() {
+    if (this.all) {
+      for (var remap of (this.all: Array)) {
+        remap.scope.removeData(this._getKey(remap.name));
+      }
+    }
+
+    this.all = [];
+  }
+}
diff --git a/src/babel/transformation/modules/system.js b/src/babel/transformation/modules/system.js
index afcb86a003..da4b410aec 100644
--- a/src/babel/transformation/modules/system.js
+++ b/src/babel/transformation/modules/system.js
@@ -82,6 +82,8 @@ export default class SystemFormatter extends AMDFormatter {
     this.exportIdentifier = file.scope.generateUidIdentifier("export");
     this.noInteropRequireExport = true;
     this.noInteropRequireImport = true;
+
+    this.remaps.clearAll();
   }
 
   _addImportSource(node, exportNode) {
@@ -137,13 +139,13 @@ export default class SystemFormatter extends AMDFormatter {
   importSpecifier(specifier, node, nodes) {
     AMDFormatter.prototype.importSpecifier.apply(this, arguments);
 
-    for (var name in this.internalRemap) {
+    for (var remap of (this.remaps.getAll(): Array)) {
       nodes.push(t.variableDeclaration("var", [
-        t.variableDeclarator(t.identifier(name), this.internalRemap[name])
+        t.variableDeclarator(t.identifier(remap.name), remap.node)
       ]));
     }
 
-    this.internalRemap = object();
+    this.remaps.clearAll();
 
     this._addImportSource(last(nodes), node);
   }
diff --git a/src/babel/transformation/transformers/es6/modules.js b/src/babel/transformation/transformers/es6/modules.js
index e83a1454c6..ba653750fb 100644
--- a/src/babel/transformation/transformers/es6/modules.js
+++ b/src/babel/transformation/transformers/es6/modules.js
@@ -21,10 +21,10 @@ export var visitor = {
 
     if (node.specifiers.length) {
       for (var specifier of (node.specifiers: Array)) {
-        file.moduleFormatter.importSpecifier(specifier, node, nodes, parent);
+        file.moduleFormatter.importSpecifier(specifier, node, nodes, scope);
       }
     } else {
-      file.moduleFormatter.importDeclaration(node, nodes, parent);
+      file.moduleFormatter.importDeclaration(node, nodes, scope);
     }
 
     if (nodes.length === 1) {
@@ -37,14 +37,14 @@ export var visitor = {
 
   ExportAllDeclaration(node, parent, scope, file) {
     var nodes = [];
-    file.moduleFormatter.exportAllDeclaration(node, nodes, parent);
+    file.moduleFormatter.exportAllDeclaration(node, nodes, scope);
     keepBlockHoist(node, nodes);
     return nodes;
   },
 
   ExportDefaultDeclaration(node, parent, scope, file) {
     var nodes = [];
-    file.moduleFormatter.exportDeclaration(node, nodes, parent);
+    file.moduleFormatter.exportDeclaration(node, nodes, scope);
     keepBlockHoist(node, nodes);
     return nodes;
   },
@@ -63,10 +63,10 @@ export var visitor = {
         declar.init = declar.init || t.identifier("undefined");
       }
 
-      file.moduleFormatter.exportDeclaration(node, nodes, parent);
+      file.moduleFormatter.exportDeclaration(node, nodes, scope);
     } else if (node.specifiers) {
       for (let i = 0; i < node.specifiers.length; i++) {
-        file.moduleFormatter.exportSpecifier(node.specifiers[i], node, nodes, parent);
+        file.moduleFormatter.exportSpecifier(node.specifiers[i], node, nodes, scope);
       }
     }
 
diff --git a/src/babel/traversal/scope/index.js b/src/babel/traversal/scope/index.js
index 7415a30f08..2a69c855ca 100644
--- a/src/babel/traversal/scope/index.js
+++ b/src/babel/traversal/scope/index.js
@@ -598,6 +598,38 @@ export default class Scope {
     }
   }
 
+  /**
+   * Set some arbitrary data on the current scope.
+   */
+
+  setData(key, val) {
+    return this.data[key] = val;
+  }
+
+  /**
+   * Recursively walk up scope tree looking for the data `key`.
+   */
+
+  getData(key) {
+    var scope = this;
+    do {
+      var data = scope.data[key];
+      if (data != null) return data;
+    } while(scope = scope.parent);
+  }
+  /**
+   * Recursively walk up scope tree looking for the data `key` and if it exists,
+   * remove it.
+   */
+
+  removeData(key) {
+    var scope = this;
+    do {
+      var data = scope.data[key];
+      if (data != null) scope.data[key] = null;
+    } while(scope = scope.parent);
+  }
+
   /**
    * Description
    */
@@ -623,6 +655,7 @@ export default class Scope {
       bindings:   object(),
       globals:    object(),
       uids:       object(),
+      data:       object(),
     };
 
     extend(this, info);
diff --git a/test/core/fixtures/transformation/es6.modules-common/loose-collision/actual.js b/test/core/fixtures/transformation/es6.modules-common/loose-collision/actual.js
new file mode 100644
index 0000000000..89934708a6
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.modules-common/loose-collision/actual.js
@@ -0,0 +1,5 @@
+if (true) {
+  import foo from "foo";
+} else {
+  import bar from "foo";
+}
diff --git a/test/core/fixtures/transformation/es6.modules-common/loose-collision/options.json b/test/core/fixtures/transformation/es6.modules-common/loose-collision/options.json
new file mode 100644
index 0000000000..1d2da25030
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.modules-common/loose-collision/options.json
@@ -0,0 +1,4 @@
+{
+  "throws": "Duplicate module declarations with the same source but in different scopes",
+  "loose": "es6.modules"
+}
diff --git a/test/core/fixtures/transformation/es6.modules-common/loose/actual.js b/test/core/fixtures/transformation/es6.modules-common/loose/actual.js
index 0c650f9545..6d06248e3c 100644
--- a/test/core/fixtures/transformation/es6.modules-common/loose/actual.js
+++ b/test/core/fixtures/transformation/es6.modules-common/loose/actual.js
@@ -1 +1,7 @@
 export var foo = 5;
+
+if (true) {
+  import bar from "bar";
+}
+
+bar;
diff --git a/test/core/fixtures/transformation/es6.modules-common/loose/expected.js b/test/core/fixtures/transformation/es6.modules-common/loose/expected.js
index 7c5d4df47b..cd9f50ef3d 100644
--- a/test/core/fixtures/transformation/es6.modules-common/loose/expected.js
+++ b/test/core/fixtures/transformation/es6.modules-common/loose/expected.js
@@ -2,4 +2,12 @@
 
 exports.__esModule = true;
 var foo = 5;
-exports.foo = foo;
\ No newline at end of file
+
+exports.foo = foo;
+if (true) {
+  var _bar = require("bar");
+
+  var _bar2 = babelHelpers.interopRequireDefault(_bar);
+}
+
+bar;