diff --git a/lib/rules/sort-prop-types.js b/lib/rules/sort-prop-types.js
index a5b96c35bc..4a79aa5407 100644
--- a/lib/rules/sort-prop-types.js
+++ b/lib/rules/sort-prop-types.js
@@ -21,6 +21,38 @@ const messages = {
   propsNotSorted: 'Prop types declarations should be sorted alphabetically',
 };
 
+function getKey(context, node) {
+  if (node.type === 'ObjectTypeProperty') {
+    return context.getSourceCode().getFirstToken(node).value;
+  }
+  if (node.key && node.key.value) {
+    return node.key.value;
+  }
+  return context.getSourceCode().getText(node.key || node.argument);
+}
+
+function getValueName(node) {
+  return node.type === 'Property' && node.value.property && node.value.property.name;
+}
+
+function isCallbackPropName(propName) {
+  return /^on[A-Z]/.test(propName);
+}
+
+function isRequiredProp(node) {
+  return getValueName(node) === 'isRequired';
+}
+
+function isShapeProp(node) {
+  return Boolean(
+    node && node.callee && node.callee.property && node.callee.property.name === 'shape'
+  );
+}
+
+function toLowerCase(item) {
+  return String(item).toLowerCase();
+}
+
 module.exports = {
   meta: {
     docs: {
@@ -71,38 +103,6 @@ module.exports = {
 
     const typeAnnotations = new Map();
 
-    function getKey(node) {
-      if (node.type === 'ObjectTypeProperty') {
-        return context.getSourceCode().getFirstToken(node).value;
-      }
-      if (node.key && node.key.value) {
-        return node.key.value;
-      }
-      return context.getSourceCode().getText(node.key || node.argument);
-    }
-
-    function getValueName(node) {
-      return node.type === 'Property' && node.value.property && node.value.property.name;
-    }
-
-    function isCallbackPropName(propName) {
-      return /^on[A-Z]/.test(propName);
-    }
-
-    function isRequiredProp(node) {
-      return getValueName(node) === 'isRequired';
-    }
-
-    function isShapeProp(node) {
-      return Boolean(
-        node && node.callee && node.callee.property && node.callee.property.name === 'shape'
-      );
-    }
-
-    function toLowerCase(item) {
-      return String(item).toLowerCase();
-    }
-
     /**
      * Checks if propTypes declarations are sorted
      * @param {Array} declarations The array of AST nodes being checked.
@@ -137,8 +137,8 @@ module.exports = {
           return decls[idx + 1];
         }
 
-        let prevPropName = getKey(prev);
-        let currentPropName = getKey(curr);
+        let prevPropName = getKey(context, prev);
+        let currentPropName = getKey(context, curr);
         const previousIsRequired = isRequiredProp(prev);
         const currentIsRequired = isRequiredProp(curr);
         const previousIsCallback = isCallbackPropName(prevPropName);