diff --git a/jmespath.js b/jmespath.js
index 0a36691..bddb0a6 100644
--- a/jmespath.js
+++ b/jmespath.js
@@ -67,6 +67,11 @@
     return false;
   }
 
+  // Ordering operators are only valid for numbers
+  function compareable(first, second) {
+    return (typeof first === 'number' && typeof second === 'number');
+  }
+
   function isFalse(obj) {
     // From the spec:
     // A false value corresponds to the following values:
@@ -985,16 +990,16 @@
                   result = !strictDeepEqual(first, second);
                   break;
                 case TOK_GT:
-                  result = first > second;
+                  result = compareable(first, second) ? first > second : null;
                   break;
                 case TOK_GTE:
-                  result = first >= second;
+                  result = compareable(first, second) ? first >= second : null;
                   break;
                 case TOK_LT:
-                  result = first < second;
+                  result = compareable(first, second) ? first < second : null;
                   break;
                 case TOK_LTE:
-                  result = first <= second;
+                  result = compareable(first, second) ? first <= second : null;
                   break;
                 default:
                   throw new Error("Unknown comparator: " + node.name);
diff --git a/test/compliance/boolean.json b/test/compliance/boolean.json
index e3fa196..1beaacb 100644
--- a/test/compliance/boolean.json
+++ b/test/compliance/boolean.json
@@ -76,7 +76,9 @@
       "False": false,
       "Number": 5,
       "EmptyList": [],
-      "Zero": 0
+      "Zero": 0,
+      "String": "foo",
+      "Null": null
     },
     "cases": [
       {
@@ -198,6 +200,30 @@
       {
         "expression": "!!Zero",
         "result": true
+      },
+      {
+        "expression": "String < Number",
+        "result": null
+      },
+      {
+        "expression": "Number < String",
+        "result": null
+      },
+      {
+        "expression": "Null < Number",
+        "result": null
+      },
+      {
+        "expression": "Number < Null",
+        "result": null
+      },
+      {
+        "expression": "Null < String",
+        "result": null
+      },
+      {
+        "expression": "String < Null",
+        "result": null
       }
     ]
   },