diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -1183,6 +1183,22 @@
     The sret type argument specifies the in memory type, which must be
     the same as the pointee type of the argument.
 
+``elementtype(<ty>)``
+
+    The ``elementtype`` argument attribute can be used to specify a pointer
+    element type in a way that is compatible with `opaque pointers
+    <OpaquePointers.html>`.
+
+    The ``elementtype`` attribute by itself does not carry any specific
+    semantics. However, certain intrinsics may require this attribute to be
+    present and assign it particular semantics. This will be documented on
+    individual intrinsics.
+
+    The attribute may only be applied to pointer typed arguments of intrinsic
+    calls. It cannot be applied to non-intrinsic calls, and cannot be applied
+    to parameters on function declarations. For non-opaque pointers, the type
+    passed to ``elementtype`` must match the pointer element type.
+
 .. _attr_align:
 
 ``align <n>`` or ``align(<n>)``