diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 55e9db3..413f4dd 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -216,14 +216,14 @@
             self.assertEqual(w.winerror, 3)
             self.assertEqual(w.strerror, 'foo')
             self.assertEqual(w.filename, 'bar')
-            self.assertEqual(str(w), "[Error 3] foo: 'bar'")
+            self.assertEqual(str(w), "[WinError 3] foo: 'bar'")
             # Unknown win error becomes EINVAL (22)
             w = OSError(0, 'foo', None, 1001)
             self.assertEqual(w.errno, 22)
             self.assertEqual(w.winerror, 1001)
             self.assertEqual(w.strerror, 'foo')
             self.assertEqual(w.filename, None)
-            self.assertEqual(str(w), "[Error 1001] foo")
+            self.assertEqual(str(w), "[WinError 1001] foo")
             # Non-numeric "errno"
             w = OSError('bar', 'foo')
             self.assertEqual(w.errno, 'bar')
diff --git a/Misc/NEWS b/Misc/NEWS
index f59b1b8..17d0c10 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -40,6 +40,9 @@
 Core and Builtins
 -----------------
 
+- Issue #15784: Modify OSError.__str__() to better distinguish between
+  errno error numbers and Windows error numbers.
+
 - Issue #15781: Fix two small race conditions in import's module locking.
 
 Library
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 74bb262..6b04700 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1016,12 +1016,12 @@
 #ifdef MS_WINDOWS
     /* If available, winerror has the priority over myerrno */
     if (self->winerror && self->filename)
-        return PyUnicode_FromFormat("[Error %S] %S: %R",
+        return PyUnicode_FromFormat("[WinError %S] %S: %R",
                                     self->winerror ? self->winerror: Py_None,
                                     self->strerror ? self->strerror: Py_None,
                                     self->filename);
     if (self->winerror && self->strerror)
-        return PyUnicode_FromFormat("[Error %S] %S",
+        return PyUnicode_FromFormat("[WinError %S] %S",
                                     self->winerror ? self->winerror: Py_None,
                                     self->strerror ? self->strerror: Py_None);
 #endif