diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index dab56ce..a3c8dcc 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -18,6 +18,13 @@
     import pty, signal
 except ImportError:
     pty = signal = None
+# Importing this module has the side-effect of changing the behavior of input().
+# Ensure that we always use the readline version (if available), so we don't get
+# different results depending on what other tests have already imported.
+try:
+    import readline
+except ImportError:
+    pass
 
 
 class Squares:
diff --git a/Misc/NEWS b/Misc/NEWS
index c216cc9..3543feb 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,10 @@
 Core and Builtins
 -----------------
 
+- Issue #13886: Fix input() to not strip out input bytes that cannot be decoded
+  using the locale encoding. Also fix sporadic failures in test_builtin due to
+  dependence on whether the readline module has previously been imported.
+
 - Issue #10156: In the interpreter's initialization phase, unicode globals
   are now initialized dynamically as needed.
 
diff --git a/Modules/readline.c b/Modules/readline.c
index 4d54dad..fd60377 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1068,7 +1068,7 @@
     char *saved_locale = strdup(setlocale(LC_CTYPE, NULL));
     if (!saved_locale)
         Py_FatalError("not enough memory to save locale");
-    setlocale(LC_CTYPE, "");
+    setlocale(LC_CTYPE, "C");
 #endif
 
     if (sys_stdin != rl_instream || sys_stdout != rl_outstream) {