diff --git a/.github/workflows/cross.yml b/.github/workflows/cross.yml
index 9d2a160f63b..2850d1b01a5 100644
--- a/.github/workflows/cross.yml
+++ b/.github/workflows/cross.yml
@@ -23,6 +23,12 @@ jobs:
     if: github.repository_owner == 'aws'
     name: cross tests ${{ matrix.target[0] }}
     runs-on: ubuntu-22.04
+    env:
+      # The flag below is set to avoid the following error with GCC 11.4.0 on the riscv64 platform:
+      #   /home/runner/work/aws-lc-rs/aws-lc-rs/aws-lc-sys/aws-lc/crypto/pem/pem_lib.c:707:11: error: 'strncmp' of strings of length 1 and 9 and bound of 9 evaluates to nonzero [-Werror=string-compare]
+      #    707 |       if (strncmp(buf, "-----END ", 9) == 0) {
+      #        |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
+      AWS_LC_SYS_CFLAGS_riscv64gc_unknown_linux_gnu: '-Wno-string-compare'
     strategy:
       fail-fast: false
       matrix:
@@ -42,7 +48,7 @@ jobs:
           - [ powerpc64-unknown-linux-gnu, 1, 0 ]
           - [ powerpc64le-unknown-linux-gnu, 1, 0 ]
           - [ riscv64gc-unknown-linux-gnu, 0, 1 ]
-          - [ s390x-unknown-linux-gnu, 0, 1 ]
+          - [ s390x-unknown-linux-gnu, 0, 0 ]
           - [ x86_64-pc-windows-gnu, 0, 1 ] # Requires release build. See: https://github.com/rust-lang/rust/issues/139380
           - [ x86_64-unknown-linux-musl, 0, 1 ]
           - [ x86_64-unknown-illumos, 0, 0 ]
@@ -62,13 +68,6 @@ jobs:
           target: ${{ matrix.target[0] }}
       - name: Set Rust toolchain override
         run: rustup override set ${{ steps.toolchain.outputs.name }}
-      # The flag below is set to avoid the following error with GCC 11.4.0 on the riscv64 platform:
-      #   /home/runner/work/aws-lc-rs/aws-lc-rs/aws-lc-sys/aws-lc/crypto/pem/pem_lib.c:707:11: error: 'strncmp' of strings of length 1 and 9 and bound of 9 evaluates to nonzero [-Werror=string-compare]
-      #    707 |       if (strncmp(buf, "-----END ", 9) == 0) {
-      #        |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
-      - if: ${{ matrix.target[0] == 'riscv64gc-unknown-linux-gnu' }}
-        run: |
-          echo 'AWS_LC_SYS_CFLAGS=-Wno-string-compare' >> "$GITHUB_ENV"
       - if: ${{ !startsWith(matrix.target[0], 'x86_64') }}
         run: |
           echo 'AWS_LC_RS_DISABLE_SLOW_TESTS=1' >> "$GITHUB_ENV"
diff --git a/aws-lc-sys/builder/main.rs b/aws-lc-sys/builder/main.rs
index 93af0274b75..20fe6eb25cf 100644
--- a/aws-lc-sys/builder/main.rs
+++ b/aws-lc-sys/builder/main.rs
@@ -496,7 +496,7 @@ impl CStdRequested {
 static mut PREGENERATED: bool = false;
 static mut AWS_LC_SYS_NO_PREFIX: bool = false;
 static mut AWS_LC_SYS_PREGENERATING_BINDINGS: bool = false;
-static mut AWS_LC_SYS_EXTERNAL_BINDGEN: bool = false;
+static mut AWS_LC_SYS_EXTERNAL_BINDGEN: Option<bool> = None;
 static mut AWS_LC_SYS_NO_ASM: bool = false;
 static mut AWS_LC_SYS_CFLAGS: String = String::new();
 static mut AWS_LC_SYS_PREBUILT_NASM: Option<bool> = None;
@@ -511,7 +511,7 @@ fn initialize() {
         AWS_LC_SYS_NO_PREFIX = env_crate_var_to_bool("NO_PREFIX").unwrap_or(false);
         AWS_LC_SYS_PREGENERATING_BINDINGS =
             env_crate_var_to_bool("PREGENERATING_BINDINGS").unwrap_or(false);
-        AWS_LC_SYS_EXTERNAL_BINDGEN = env_crate_var_to_bool("EXTERNAL_BINDGEN").unwrap_or(false);
+        AWS_LC_SYS_EXTERNAL_BINDGEN = env_crate_var_to_bool("EXTERNAL_BINDGEN");
         AWS_LC_SYS_NO_ASM = env_crate_var_to_bool("NO_ASM").unwrap_or(false);
         AWS_LC_SYS_CFLAGS = optional_env_optional_crate_target("CFLAGS").unwrap_or_default();
         AWS_LC_SYS_PREBUILT_NASM = env_crate_var_to_bool("PREBUILT_NASM");
@@ -523,7 +523,9 @@ fn initialize() {
             optional_env_crate_target("EFFECTIVE_TARGET").unwrap_or_default();
     }
 
-    if !is_external_bindgen() && (is_pregenerating_bindings() || !has_bindgen_feature()) {
+    if !is_external_bindgen_requested().unwrap_or(false)
+        && (is_pregenerating_bindings() || !has_bindgen_feature())
+    {
         let target = effective_target();
         let supported_platform = match target.as_str() {
             "aarch64-apple-darwin"
@@ -553,7 +555,7 @@ fn initialize() {
 fn is_bindgen_required() -> bool {
     is_no_prefix()
         || is_pregenerating_bindings()
-        || is_external_bindgen()
+        || is_external_bindgen_requested().unwrap_or(false)
         || has_bindgen_feature()
         || !has_pregenerated()
 }
@@ -574,7 +576,7 @@ fn is_pregenerating_bindings() -> bool {
     unsafe { AWS_LC_SYS_PREGENERATING_BINDINGS }
 }
 
-fn is_external_bindgen() -> bool {
+fn is_external_bindgen_requested() -> Option<bool> {
     unsafe { AWS_LC_SYS_EXTERNAL_BINDGEN }
 }
 
@@ -655,7 +657,7 @@ fn is_crt_static() -> bool {
 
 bindgen_available!(
     fn handle_bindgen(manifest_dir: &Path, prefix: &Option<String>) -> bool {
-        if internal_bindgen_supported() && !is_external_bindgen() {
+        if internal_bindgen_supported() && !is_external_bindgen_requested().unwrap_or(false) {
             emit_warning(&format!(
                 "Generating bindings - internal bindgen. Platform: {}",
                 effective_target()
@@ -704,7 +706,7 @@ fn main() {
             let src_bindings_path = Path::new(&manifest_dir)
                 .join("src")
                 .join(format!("{}.rs", target_platform_prefix("crypto")));
-            if is_external_bindgen() {
+            if is_external_bindgen_requested().unwrap_or(false) {
                 invoke_external_bindgen(&manifest_dir, &prefix, &src_bindings_path).unwrap();
             } else {
                 generate_src_bindings(&manifest_dir, &prefix, &src_bindings_path);
@@ -827,6 +829,12 @@ impl Debug for BindingOptions {
 }
 
 fn verify_bindgen() -> Result<(), String> {
+    if !is_external_bindgen_requested().unwrap_or(true) {
+        return Err(
+            "external bindgen usage prevented by AWS_LC_SYS_EXTERNAL_BINDGEN=0".to_string(),
+        );
+    }
+
     let result = execute_command("bindgen".as_ref(), &["--version".as_ref()]);
     if !result.status {
         if result.executed {