diff --git a/barretenberg/cpp/bootstrap.sh b/barretenberg/cpp/bootstrap.sh
index 7a38e0bd4f80..a4c70bba834c 100755
--- a/barretenberg/cpp/bootstrap.sh
+++ b/barretenberg/cpp/bootstrap.sh
@@ -7,6 +7,7 @@ else
   export native_preset=${NATIVE_PRESET:-clang20-no-avm}
 fi
 export hash=$(hash_str $(../../avm-transpiler/bootstrap.sh hash) $(cache_content_hash .rebuild_patterns))
+export native_build_dir=$(scripts/preset-build-dir)
 
 # Injects version number into a given bb binary.
 # Means we don't actually need to rebuild bb to release a new version if code hasn't changed.
diff --git a/barretenberg/cpp/cmake/arch.cmake b/barretenberg/cpp/cmake/arch.cmake
index fe6488cbce3f..cf44d66be334 100644
--- a/barretenberg/cpp/cmake/arch.cmake
+++ b/barretenberg/cpp/cmake/arch.cmake
@@ -9,7 +9,12 @@ endif()
 # Use 'skylake' on x86_64 (matches our cross-compile presets) and 'generic' on ARM
 # to avoid emitting CPU-specific instructions (e.g. SVE on Graviton) that break on
 # other ARM machines like Apple Silicon.
-if(NOT WASM AND NOT TARGET_ARCH)
+#
+# Skip auto-detection when cross-compiling: Zig cross-compile presets already
+# control the target CPU via -target and -mcpu flags. Adding -march here would
+# either pick the wrong arch (e.g. skylake on an x86 host targeting ARM) or
+# conflict with the preset's -mcpu (e.g. -march=generic overriding -mcpu=apple_a14).
+if(NOT WASM AND NOT TARGET_ARCH AND NOT CMAKE_CROSSCOMPILING)
     if(ARM)
         set(TARGET_ARCH "generic")
     else()