diff --git a/.github/workflows/mac_codesign.yml b/.github/workflows/mac_codesign.yml
index 728c92bc2..e1b5c7c03 100644
--- a/.github/workflows/mac_codesign.yml
+++ b/.github/workflows/mac_codesign.yml
@@ -9,9 +9,14 @@ jobs:
     environment: macos-codesign
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@1.79
+      - name: Install Rust 1.73.0
+        uses: dtolnay/rust-toolchain@1.73.0
         with:
-          targets: aarch64-apple-darwin,x86_64-apple-darwin
+          targets: x86_64-apple-darwin
+      - name: Install Rust 1.79
+        uses: dtolnay/rust-toolchain@1.79
+        with:
+          targets: aarch64-apple-darwin
       - name: build-and-codesign
         run: |
           cargo install apple-codesign
diff --git a/build_tools/make_pkg.sh b/build_tools/make_pkg.sh
index 8f06e2dbc..a6ee416f0 100755
--- a/build_tools/make_pkg.sh
+++ b/build_tools/make_pkg.sh
@@ -26,6 +26,12 @@ NOTARIZE=
 ARM64_DEPLOY_TARGET='MACOSX_DEPLOYMENT_TARGET=11.0'
 X86_64_DEPLOY_TARGET='MACOSX_DEPLOYMENT_TARGET=10.9'
 
+# As of this writing, the most recent Rust release supports macOS back to 10.12.
+# The first supported version of macOS on arm64 is 10.15, so any Rust is fine for arm64.
+# We wish to support back to 10.9 on x86-64; the last version of Rust to support that is
+# version 1.73.0.
+RUST_VERSION_X86_64=1.73.0
+
 while getopts "sf:i:p:e:nj:" opt; do
   case $opt in
     s) SIGN=1;;
@@ -83,11 +89,13 @@ mkdir -p "$PKGDIR/build_x86_64" "$PKGDIR/build_arm64" "$PKGDIR/root" "$PKGDIR/in
 }
 
 # Build for x86-64 but do not install; instead we will make some fat binaries inside the root.
+# Set RUST_VERSION_X86_64 to the last version of Rust that supports macOS 10.9.
 { cd "$PKGDIR/build_x86_64" \
   && cmake \
         -DCMAKE_BUILD_TYPE=RelWithDebInfo \
         -DCMAKE_EXE_LINKER_FLAGS="-Wl,-ld_classic" \
         -DWITH_GETTEXT=OFF \
+        -DRust_TOOLCHAIN="$RUST_VERSION_X86_64" \
         -DRust_CARGO_TARGET=x86_64-apple-darwin \
         -DCMAKE_OSX_ARCHITECTURES='arm64;x86_64' \
         -DFISH_USE_SYSTEM_PCRE2=OFF "$SRC_DIR" \