diff --git a/jmespath/functions.py b/jmespath/functions.py
index 627b569d..38dfa0c9 100644
--- a/jmespath/functions.py
+++ b/jmespath/functions.py
@@ -316,14 +316,19 @@ def _func_sort_by(self, array, expref):
         # either a string of a number.  We then create a key function
         # that validates that type, which requires that remaining array
         # elements resolve to the same type as the first element.
+        # The type check is done on the resolved key, not on the array
+        # element, because that's the value the signature constrains.
+        keyfunc = self._create_key_func(expref,
+                                        ['number', 'string'],
+                                        'sort_by')
+        required_key = keyfunc(array[0])
         required_type = self._convert_to_jmespath_type(
-            type(expref.visit(expref.expression, array[0])).__name__)
+            type(required_key).__name__)
         if required_type not in ['number', 'string']:
             raise exceptions.JMESPathTypeError(
-                'sort_by', array[0], required_type, ['string', 'number'])
-        keyfunc = self._create_key_func(expref,
-                                        [required_type],
-                                        'sort_by')
+                'sort_by', required_key, required_type,
+                ['string', 'number'])
+        keyfunc = self._create_key_func(expref, [required_type], 'sort_by')
         return list(sorted(array, key=keyfunc))
 
     @signature({'types': ['array']}, {'types': ['expref']})
diff --git a/tests/test_functions.py b/tests/test_functions.py
index a352d69e..0dfad824 100644
--- a/tests/test_functions.py
+++ b/tests/test_functions.py
@@ -55,3 +55,13 @@ def test_variadic_is_pluralized(self):
         self.assertEqual(
             str(exception),
             'Expected at least 1 argument for function not_null(), received 0')
+
+    def test_sort_by_reports_the_resolved_key_in_type_errors(self):
+        # The spec defines sort_by as sort_by(array, expression->number|
+        # expression->string), so the value that has the invalid type is the
+        # value the expression resolved to, not the array element it was
+        # resolved against.  min_by/max_by already report the resolved key.
+        with self.assertRaises(exceptions.JMESPathTypeError) as e:
+            jmespath.search('sort_by(@, &k)', [{'k': [1, 2]}])
+        self.assertIn('invalid type for value: [1, 2]', str(e.exception))
+        self.assertIn('received: "array"', str(e.exception))