diff --git a/src/items/external-blocks.md b/src/items/external-blocks.md
index 25ae37bc3..0476e7366 100644
--- a/src/items/external-blocks.md
+++ b/src/items/external-blocks.md
@@ -91,6 +91,8 @@ There are also some platform-specific ABI strings:
 * `extern "vectorcall"` -- The `vectorcall` ABI -- corresponds to MSVC's
   `__vectorcall` and clang's `__attribute__((vectorcall))`
 * `extern "efiapi"` -- The ABI used for [UEFI] functions.
+* `extern "thiscall"` -- The default for C++ member functions on MSVC -- corresponds to MSVC's
+  `__thiscall` and GCC and clang's `__attribute__((thiscall))`
 
 ## Variadic functions