diff --git a/pkgs/by-name/mi/mirth/package.nix b/pkgs/by-name/mi/mirth/package.nix
index 759d556cd217..23036eac3194 100644
--- a/pkgs/by-name/mi/mirth/package.nix
+++ b/pkgs/by-name/mi/mirth/package.nix
@@ -34,6 +34,14 @@ stdenv.mkDerivation {
   nativeBuildInputs = [ makeBinaryWrapper ];
 
   postPatch = ''
+    ${lib.optionalString (with stdenv.buildPlatform; isAarch64 && isLinux) /* sh */ ''
+      # Bug report: https://todo.sr.ht/~typeswitch/mirth/16
+      substituteInPlace bin/mirth0.c \
+        --replace-fail "WRAP_I63(24LL);" "WRAP_I63(16LL);"
+      substituteInPlace lib/std/world.mth \
+        --replace-fail "Linux -> 24u," "Linux -> running-arch Arch.ARM64 = if(16u, 24u),"
+    ''}
+
     # Replace hard-coded GCC with stdenv’s C compiler.
     # NOTE: newer GCC requires optimization level ≥1 to use fortity. -O1 is
     # fast enough as a default for the compiler stages.
@@ -51,7 +59,8 @@ stdenv.mkDerivation {
     "bin/mirth3"
   ];
 
-  doCheck = true;
+  # st_mode substitution intentionally diverges from the pre-generated mirth0.c
+  doCheck = with stdenv.buildPlatform; !(isAarch64 && isLinux);
 
   installPhase = ''
     runHook preInstall