diff --git a/docs/BitCodeFormat.rst b/docs/BitCodeFormat.rst
index 065f9c3d49d..6e491c6e285 100644
--- a/docs/BitCodeFormat.rst
+++ b/docs/BitCodeFormat.rst
@@ -1067,6 +1067,7 @@ The integer codes are mapped to well-known attributes as follows.
 * code 65: ``preallocated``
 * code 66: ``no_merge``
 * code 67: ``null_pointer_is_valid``
+* code 68: ``noundef``
 
 .. note::
   The ``allocsize`` attribute has a special encoding for its arguments. Its two
diff --git a/docs/LangRef.rst b/docs/LangRef.rst
index cc2f6d1b3a0..566d761d307 100644
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@@ -1252,6 +1252,12 @@ Currently, only the following parameter attributes are defined:
     only valid on intrinsic declarations and cannot be applied to a
     call site or arbitrary function.
 
+``noundef``
+    This attribute applies to parameters and return values. If the value
+    representation contains any undefined or poison bits, the behavior is
+    undefined. Note that this does not refer to padding introduced by the
+    type's storage representation.
+
 .. _gc:
 
 Garbage Collector Strategy Names
@@ -3657,6 +3663,11 @@ behavior. Notably this includes (but is not limited to):
 -  The condition operand of a :ref:`br <i_br>` instruction.
 -  The callee operand of a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
    instruction.
+-  The parameter operand of a :ref:`call <i_call>` or :ref:`invoke <i_invoke>`
+   instruction, when the function or invoking call site has a ``noundef``
+   attribute in the corresponding position.
+-  The operand of a :ref:`ret <i_ret>` instruction if the function or invoking
+   call site has a `noundef` attribute in the return value position.
 
 Here are some examples: