diff --git a/Lib/json/encoder.py b/Lib/json/encoder.py
index f5eeed7..97ffe8e 100644
--- a/Lib/json/encoder.py
+++ b/Lib/json/encoder.py
@@ -28,7 +28,7 @@
     #ESCAPE_DCT.setdefault(chr(i), '\\u%04x' % (i,))
 
 INFINITY = float('inf')
-FLOAT_REPR = repr
+FLOAT_REPR = float.__repr__
 
 def encode_basestring(s):
     """Return a JSON representation of a Python string
diff --git a/Lib/json/tests/test_float.py b/Lib/json/tests/test_float.py
index 049f9ae..c10381d 100644
--- a/Lib/json/tests/test_float.py
+++ b/Lib/json/tests/test_float.py
@@ -32,6 +32,17 @@
                 self.assertNotEqual(res[0], res[0])
             self.assertRaises(ValueError, self.dumps, [val], allow_nan=False)
 
+    def test_float_subclasses_use_float_repr(self):
+        # Issue 27934.
+        class PeculiarFloat(float):
+            def __repr__(self):
+                return "I'm not valid JSON"
+            def __str__(self):
+                return "Neither am I"
+
+        val = PeculiarFloat(3.2)
+        self.assertEqual(self.loads(self.dumps(val)), val)
+
 
 class TestPyFloat(TestFloat, PyTest): pass
 class TestCFloat(TestFloat, CTest): pass