diff --git a/cbits/aarch64.h b/cbits/aarch64.h
new file mode 100644
--- /dev/null
+++ b/cbits/aarch64.h
@@ -0,0 +1,5 @@
+#include <stdint.h>
+
+uint64_t umulh(uint64_t x, uint64_t y);
+
+uint64_t umodh(uint64_t lo, uint64_t hi, uint64_t m);
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,7 @@
+# 0.2.0.1
+
+* Fix build on `aarch64`.
+
 # 0.2.0.0
 
 * Breaking change: redesign `GcdDomain` and `Euclidean` instances.
diff --git a/mod.cabal b/mod.cabal
--- a/mod.cabal
+++ b/mod.cabal
@@ -1,5 +1,5 @@
 name:          mod
-version:       0.2.0.0
+version:       0.2.0.1
 cabal-version: >=1.10
 build-type:    Simple
 license:       MIT
@@ -19,6 +19,7 @@
 extra-source-files:
   changelog.md
   README.md
+  cbits/aarch64.h
 
 source-repository head
   type: git