diff --git a/lib/rules/sort-prop-types.js b/lib/rules/sort-prop-types.js
index b3c04f5482..817e4123d7 100644
--- a/lib/rules/sort-prop-types.js
+++ b/lib/rules/sort-prop-types.js
@@ -3,6 +3,10 @@
  */
 'use strict';
 
+var find = require('array.prototype.find');
+
+var variableUtil = require('../util/variable');
+
 // ------------------------------------------------------------------------------
 // Rule Definition
 // ------------------------------------------------------------------------------
@@ -150,11 +154,32 @@ module.exports = {
       },
 
       MemberExpression: function(node) {
-        if (isPropTypesDeclaration(node.property)) {
-          var right = node.parent.right;
-          if (right && right.type === 'ObjectExpression') {
-            checkSorted(right.properties);
-          }
+        if (!isPropTypesDeclaration(node.property)) {
+          return;
+        }
+        var right = node.parent.right;
+        var declarations;
+        switch (right && right.type) {
+          case 'ObjectExpression':
+            declarations = right.properties;
+            break;
+          case 'Identifier':
+            var variable = find(variableUtil.variablesInScope(context), function (item) {
+              return item.name === right.name;
+            });
+            if (
+              !variable || !variable.defs[0] ||
+              !variable.defs[0].node.init || !variable.defs[0].node.init.properties
+            ) {
+              break;
+            }
+            declarations = variable.defs[0].node.init.properties;
+            break;
+          default:
+            break;
+        }
+        if (declarations) {
+          checkSorted(declarations);
         }
       },
 
diff --git a/tests/lib/rules/sort-prop-types.js b/tests/lib/rules/sort-prop-types.js
index d18b8aa144..fd1fe835ba 100644
--- a/tests/lib/rules/sort-prop-types.js
+++ b/tests/lib/rules/sort-prop-types.js
@@ -323,6 +323,15 @@ ruleTester.run('sort-prop-types', rule, {
       '}'
     ].join('\n'),
     parser: 'babel-eslint'
+  }, {
+    code: [
+      'const propTypes = require(\'./externalPropTypes\')',
+      'const TextFieldLabel = (props) => {',
+      '  return <div />;',
+      '};',
+      'TextFieldLabel.propTypes = propTypes;'
+    ].join('\n'),
+    parserOptions: parserOptions
   }],
 
   invalid: [{
@@ -624,5 +633,23 @@ ruleTester.run('sort-prop-types', rule, {
       column: 5,
       type: 'Property'
     }]
+  }, {
+    code: [
+      'const propTypes = {',
+      '  b: PropTypes.string,',
+      '  a: PropTypes.string,',
+      '};',
+      'const TextFieldLabel = (props) => {',
+      '  return <div />;',
+      '};',
+      'TextFieldLabel.propTypes = propTypes;'
+    ].join('\n'),
+    parserOptions: parserOptions,
+    errors: [{
+      message: ERROR_MESSAGE,
+      line: 3,
+      column: 3,
+      type: 'Property'
+    }]
   }]
 });