diff --git a/docs/users_guide/9.2.5-notes.rst b/docs/users_guide/9.2.5-notes.rst
index fca1f59d17472301c5b66eda64667c90bc781150..54e5a1a2c65630b5e09bf816312d1f02fc40b9d0 100644
--- a/docs/users_guide/9.2.5-notes.rst
+++ b/docs/users_guide/9.2.5-notes.rst
@@ -21,6 +21,8 @@ Compiler
 
 - Fix a code generation panic when using SIMD types with unboxed sums (:ghc-ticket:`22187`).
 
+- Fix a code generation bug with the native code generator on aarch64 darwin leading to runtime segmentation faults due to an incorrect ABI (:ghc-ticket:`21964`)
+
 Runtime system
 --------------
 
diff --git a/includes/CodeGen.Platform.hs b/includes/CodeGen.Platform.hs
index 0dfac62a3f125d87fc68d990decfb83c0c511b62..ebec0212bd0f48071ae51673fdeb7b86c156936d 100644
--- a/includes/CodeGen.Platform.hs
+++ b/includes/CodeGen.Platform.hs
@@ -1028,6 +1028,14 @@ freeReg 29 = False
 -- ip0 -- used for spill offset computations
 freeReg 16 = False
 
+#if defined(darwin_HOST_OS) || defined(ios_HOST_OS)
+-- x18 is reserved by the platform on Darwin/iOS, and can not be used
+-- More about ARM64 ABI that Apple platforms support:
+-- https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms
+-- https://github.com/Siguza/ios-resources/blob/master/bits/arm64.md
+freeReg 18 = False
+#endif
+
 # if defined(REG_Base)
 freeReg REG_Base  = False
 # endif