diff --git a/django/template/defaultfilters.py b/django/template/defaultfilters.py
index 8319c66eee..5564ee6fcc 100644
--- a/django/template/defaultfilters.py
+++ b/django/template/defaultfilters.py
@@ -858,6 +858,10 @@ def filesizeformat(bytes):
     TB = 1 << 40
     PB = 1 << 50
 
+    negative = bytes < 0
+    if negative:
+        bytes = -bytes  # Allow formatting of negative numbers.
+
     if bytes < KB:
         value = ungettext("%(size)d byte", "%(size)d bytes", bytes) % {'size': bytes}
     elif bytes < MB:
@@ -871,6 +875,8 @@ def filesizeformat(bytes):
     else:
         value = ugettext("%s PB") % filesize_number_format(bytes / PB)
 
+    if negative:
+        value = "-%s" % value
     return avoid_wrapping(value)
 
 
diff --git a/tests/template_tests/filter_tests/test_filesizeformat.py b/tests/template_tests/filter_tests/test_filesizeformat.py
index c94da8c8d6..9d143ca100 100644
--- a/tests/template_tests/filter_tests/test_filesizeformat.py
+++ b/tests/template_tests/filter_tests/test_filesizeformat.py
@@ -39,3 +39,7 @@ class FunctionTests(SimpleTestCase):
             self.assertEqual(filesizeformat(complex(1, -1)), '0\xa0Bytes')
             self.assertEqual(filesizeformat(""), '0\xa0Bytes')
             self.assertEqual(filesizeformat("\N{GREEK SMALL LETTER ALPHA}"), '0\xa0Bytes')
+
+    def test_negative_numbers(self):
+        self.assertEqual(filesizeformat(-100), '-100\xa0bytes')
+        self.assertEqual(filesizeformat(-1024 * 1024 * 50), '-50.0\xa0MB')