diff --git a/Makefile b/Makefile
index db042c9b4..3de1e4efe 100644
--- a/Makefile
+++ b/Makefile
@@ -123,6 +123,8 @@ MD_FILES_FIND = find . -type f -name '*.md' \
 PROVER_TOOLS_SOURCE ?= git+https://github.com/leynos/rust-prover-tools@b07ef696f8373d54ae68e517d39d47a5d27a5bd5
 PROVER_TOOLS ?= uv tool run --from $(PROVER_TOOLS_SOURCE) prover-tools
 RUSTDOC_FLAGS ?= --cfg docsrs -D warnings
+unexport RUSTDOC_FLAGS
+export RUSTDOCFLAGS := $(value RUSTDOC_FLAGS)
 VERUS_FLAGS ?=
 VERUS_INSTALL_FLAGS ?=
 WHITAKER ?= whitaker
@@ -168,7 +170,7 @@ lint-python: ## Run Ruff, Pylint, the df12 house lints, and ambrleaks over the P
 	$(AMBRLEAKS) $(PYTHON_SOURCES)
 
 lint-clippy: ## Run rustdoc and Clippy with warnings denied
-	RUSTDOCFLAGS="$(RUSTDOC_FLAGS)" RUSTFLAGS="$${RUSTFLAGS:+$$RUSTFLAGS }-D warnings" $(CARGO) doc --workspace --no-deps
+	RUSTFLAGS="$${RUSTFLAGS:+$$RUSTFLAGS }-D warnings" $(CARGO) doc --workspace --no-deps
 	RUSTFLAGS="$${RUSTFLAGS:+$$RUSTFLAGS }-D warnings" $(CARGO) clippy $(CLIPPY_FLAGS)
 
 lint-whitaker: ## Run the Whitaker Dylint suite with warnings denied
@@ -180,7 +182,7 @@ lint-whitaker: ## Run the Whitaker Dylint suite with warnings denied
 doc-coverage: doc-coverage-test ## Verify aggregate Rustdoc doc-comment coverage meets the threshold
 	# Runs under the uv-pinned baseline interpreter, not the system python3:
 	# the scripts target Python 3.14 syntax and semantics.
-	@RUSTDOCFLAGS="$${RUSTDOC_FLAGS}" $(UV_ENV) $(UV) run --no-project --python $(PYTHON_BASELINE) \
+	@$(UV_ENV) $(UV) run --no-project --python $(PYTHON_BASELINE) \
 		scripts/doc-coverage.py --toolchain "$$DOC_COVERAGE_TOOLCHAIN" --threshold "$$DOC_COVERAGE_THRESHOLD"
 
 doc-coverage-test: ## Run documentation-coverage pytest modules
diff --git a/docs/developers-guide.md b/docs/developers-guide.md
index 980cc7999..4a55fbde5 100644
--- a/docs/developers-guide.md
+++ b/docs/developers-guide.md
@@ -1507,6 +1507,12 @@ The fragment sets the `codegen-backend` unstable flag,
   `rustflags` in a Cargo configuration file, so the `dev-*` targets
   deliberately do not set it. Exporting `RUSTFLAGS` in the shell silently
   disables `mold` for these targets.
+- **`RUSTDOC_FLAGS`.** Make defaults this caller-overridable variable to
+  `--cfg docsrs -D warnings` and exports it as Cargo's supported `RUSTDOCFLAGS`
+  environment variable for `make doctest`, the rustdoc stage of
+  `make lint-clippy`, and `make doc-coverage`. The unsupported `RUSTDOC_FLAGS`
+  name is not exported, so Cargo cannot warn about it. Caller overrides retain
+  their literal contents, including quotes in Rust `--cfg` values.
 - **Release and packaging.** `make release` and everything under
   `.github/workflows/build-and-package.yml` use the release profile, the LLVM
   backend, and the platform linker. Cranelift is applied to the `dev` profile
diff --git a/tests/makefile_test_target.rs b/tests/makefile_test_target.rs
index 456415a65..f8767af82 100644
--- a/tests/makefile_test_target.rs
+++ b/tests/makefile_test_target.rs
@@ -135,6 +135,9 @@ fn check_fmt_portably_skips_markdown_validation_without_files() -> Result<()> {
 #[path = "makefile_test_target/rustflags.rs"]
 mod rustflags;
 
+#[path = "makefile_test_target/rustdocflags.rs"]
+mod rustdocflags;
+
 /// Returns every nextest profile override.
 fn all_profile_overrides(config: &Value) -> impl Iterator<Item = &Value> {
     config
diff --git a/tests/makefile_test_target/rustdocflags.rs b/tests/makefile_test_target/rustdocflags.rs
new file mode 100644
index 000000000..eae560078
--- /dev/null
+++ b/tests/makefile_test_target/rustdocflags.rs
@@ -0,0 +1,266 @@
+//! Contract model for Cargo's Rustdoc environment in Makefile recipes.
+//!
+//! The caller-overridable `RUSTDOC_FLAGS` Make variable carries the shared
+//! default Rustdoc configuration, but Cargo accepts only `RUSTDOCFLAGS`.
+//! Make exports the supported name directly, which preserves literal caller
+//! values without re-parsing them in a shell. It explicitly unexports the
+//! unsupported name, preventing Cargo from warning about it. The Unix
+//! behavioural test exercises that real Make-to-Cargo boundary with a fake
+//! Cargo executable; static checks keep the safe export shape intact.
+
+use super::{read_repo_file, target_recipe};
+use anyhow::{Context, Result, ensure};
+use camino::Utf8Path;
+
+#[cfg(unix)]
+use assert_cmd::Command;
+#[cfg(unix)]
+use proptest::prelude::*;
+#[cfg(unix)]
+use std::path::{Path, PathBuf};
+#[cfg(unix)]
+use tempfile::tempdir;
+#[cfg(unix)]
+use test_support::{fs, write_exec_with_content};
+
+/// The caller-overridable Make default for the Rustdoc configuration.
+const RUSTDOC_FLAGS_DEFAULT: &str = "RUSTDOC_FLAGS ?= --cfg docsrs -D warnings";
+/// The directive that prevents Cargo from receiving its unsupported name.
+const RUSTDOC_FLAGS_UNEXPORT: &str = "unexport RUSTDOC_FLAGS";
+/// The safe Make-level mapping to Cargo's supported environment variable.
+const RUSTDOCFLAGS_EXPORT: &str = "export RUSTDOCFLAGS := $(value RUSTDOC_FLAGS)";
+
+/// An override whose shell-sensitive values must reach Rustdoc unchanged.
+#[cfg(unix)]
+const SHELL_SENSITIVE_RUSTDOC_FLAGS: &str = r#"--cfg marker="price$5 \"path\\name\"; &"#;
+
+/// Describe one caller-supplied Rustdoc override source and value.
+#[cfg(unix)]
+struct RustdocOverride<'flags> {
+    /// Store the exact Rustdoc flags supplied by the caller.
+    rustdoc_flags: &'flags str,
+    /// Identify where Make receives the caller override.
+    source: &'static str,
+    /// Distinguish a Make command-line assignment from an environment value.
+    command_line: bool,
+}
+
+#[test]
+fn behavioural_rustdocflags_default_preserves_rustdoc_warning_denial() -> Result<()> {
+    let makefile = read_repo_file(Utf8Path::new("Makefile"))?;
+    ensure!(
+        makefile.lines().any(|line| line == RUSTDOC_FLAGS_DEFAULT),
+        "Makefile should retain {RUSTDOC_FLAGS_DEFAULT:?}"
+    );
+    Ok(())
+}
+
+#[test]
+fn behavioural_make_exports_supported_rustdocflags_after_unexporting_unsupported_name() -> Result<()>
+{
+    let makefile = read_repo_file(Utf8Path::new("Makefile"))?;
+    let default_index = makefile
+        .lines()
+        .position(|line| line == RUSTDOC_FLAGS_DEFAULT)
+        .context("Makefile should declare the RUSTDOC_FLAGS default")?;
+    let unexport_index = makefile
+        .lines()
+        .position(|line| line == RUSTDOC_FLAGS_UNEXPORT)
+        .context("Makefile should unexport the unsupported RUSTDOC_FLAGS name")?;
+    let export_index = makefile
+        .lines()
+        .position(|line| line == RUSTDOCFLAGS_EXPORT)
+        .context("Makefile should export Cargo's supported RUSTDOCFLAGS name")?;
+
+    ensure!(
+        default_index < unexport_index && unexport_index < export_index,
+        "the RUSTDOC_FLAGS default, unexport, and supported export must remain ordered"
+    );
+    Ok(())
+}
+
+#[test]
+fn behavioural_rustdoc_consumers_rely_on_the_safe_make_export() -> Result<()> {
+    let makefile = read_repo_file(Utf8Path::new("Makefile"))?;
+    for target in ["doctest", "lint-clippy", "doc-coverage"] {
+        let recipe = target_recipe(&makefile, target)
+            .with_context(|| format!("Makefile should declare a {target} target"))?;
+        ensure!(
+            !recipe.contains("RUSTDOCFLAGS="),
+            "{target} must rely on Make's exported RUSTDOCFLAGS rather than interpolate flags in a shell: {recipe:?}"
+        );
+    }
+    Ok(())
+}
+
+#[test]
+fn behavioural_makefile_never_exports_or_shell_expands_rustdoc_flags() -> Result<()> {
+    let makefile = read_repo_file(Utf8Path::new("Makefile"))?;
+    for (line_number, line) in makefile.lines().enumerate() {
+        let is_recipe = line.starts_with('\t');
+        ensure!(
+            !line.trim_start().starts_with("export RUSTDOC_FLAGS"),
+            "Makefile line {} must not export unsupported RUSTDOC_FLAGS: {line:?}",
+            line_number + 1
+        );
+        ensure!(
+            !(is_recipe && line.contains("$${RUSTDOC_FLAGS}")),
+            "Makefile recipe line {} must not shell-expand RUSTDOC_FLAGS: {line:?}",
+            line_number + 1
+        );
+        ensure!(
+            !(is_recipe && line.contains("RUSTDOC_FLAGS=") && line.contains("$(CARGO)")),
+            "Makefile recipe line {} must not pass unsupported RUSTDOC_FLAGS to Cargo: {line:?}",
+            line_number + 1
+        );
+    }
+    Ok(())
+}
+
+/// Run `doctest` with a caller-supplied Rustdoc override through one source.
+#[cfg(unix)]
+fn run_doctest_with_override(
+    fake_cargo: &Path,
+    log: &Path,
+    override_config: &RustdocOverride<'_>,
+) -> Result<String> {
+    let mut make = Command::new("make");
+    make.current_dir(env!("CARGO_MANIFEST_DIR"))
+        .arg("--no-print-directory")
+        .arg("-f")
+        .arg("Makefile")
+        .env("CARGO", fake_cargo)
+        .env("RUSTDOC_ENVIRONMENT_LOG", log);
+    if override_config.command_line {
+        make.arg(format!("RUSTDOC_FLAGS={}", override_config.rustdoc_flags));
+    } else {
+        make.env("RUSTDOC_FLAGS", override_config.rustdoc_flags);
+    }
+    make.arg("doctest");
+
+    let output = make.output().with_context(|| {
+        format!(
+            "run doctest with a {} Rustdoc override",
+            override_config.source
+        )
+    })?;
+    ensure!(
+        output.status.success(),
+        "doctest with a {} override should call fake Cargo successfully: {}",
+        override_config.source,
+        String::from_utf8_lossy(&output.stderr)
+    );
+    fs::read_to_string(log).context("read fake Cargo environment log")
+}
+
+/// Assert that Cargo receives the exact supported Rustdoc configuration.
+#[cfg(unix)]
+fn assert_doctest_record(record: &str, rustdoc_flags: &str, source: &str) -> Result<()> {
+    let mut fields = record.lines().map(|line| {
+        line.split_once('\t')
+            .with_context(|| format!("malformed fake Cargo record {line:?}"))
+    });
+    let cargo_rustdocflags = fields
+        .next()
+        .transpose()?
+        .context("fake Cargo record should include RUSTDOCFLAGS")?;
+    let unsupported = fields
+        .next()
+        .transpose()?
+        .context("fake Cargo record should include RUSTDOC_FLAGS presence")?;
+    let arguments = fields
+        .next()
+        .transpose()?
+        .context("fake Cargo record should include arguments")?;
+
+    ensure!(
+        cargo_rustdocflags == ("rustdocflags", rustdoc_flags),
+        "a {source} override must retain its literal Rustdoc value, found {cargo_rustdocflags:?}"
+    );
+    ensure!(
+        unsupported == ("unsupported", ""),
+        "a {source} override must not leak RUSTDOC_FLAGS to Cargo, found {unsupported:?}"
+    );
+    ensure!(
+        arguments.0 == "arguments"
+            && arguments
+                .1
+                .contains("test --workspace --doc --all-features"),
+        "doctest should invoke Cargo's documentation-test arguments, found {arguments:?}"
+    );
+    Ok(())
+}
+
+/// Create a Cargo stand-in that records its environment and arguments.
+#[cfg(unix)]
+fn write_fake_cargo(directory: &Path) -> Result<PathBuf> {
+    write_exec_with_content(
+        directory,
+        "cargo",
+        concat!(
+            "#!/bin/sh\n",
+            ": \"${RUSTDOC_ENVIRONMENT_LOG:?}\"\n",
+            "{\n",
+            "  printf 'rustdocflags\\t%s\\n' \"${RUSTDOCFLAGS-}\"\n",
+            "  printf 'unsupported\\t%s\\n' \"${RUSTDOC_FLAGS+present}\"\n",
+            "  printf 'arguments\\t%s\\n' \"$*\"\n",
+            "} > \"$RUSTDOC_ENVIRONMENT_LOG\"\n"
+        ),
+    )
+    .context("write fake Cargo executable")
+}
+
+/// Generate valid, shell-sensitive Rustdoc overrides with bounded entropy.
+#[cfg(unix)]
+fn rustdoc_flags_strategy() -> impl Strategy<Value = String> {
+    "[a-z]{0,12}".prop_map(|suffix| format!(r#"--cfg marker="price$5 \"path\\name\"; & {suffix}""#))
+}
+
+#[cfg(unix)]
+#[test]
+fn behavioural_doctest_passes_shell_sensitive_overrides_only_as_rustdocflags() -> Result<()> {
+    let temporary = tempdir().context("create fake Cargo directory")?;
+    let log = temporary.path().join("cargo-environment.log");
+    let fake_cargo = write_fake_cargo(temporary.path())?;
+
+    for (source, command_line) in [("environment", false), ("command line", true)] {
+        let override_config = RustdocOverride {
+            rustdoc_flags: SHELL_SENSITIVE_RUSTDOC_FLAGS,
+            source,
+            command_line,
+        };
+        let record = run_doctest_with_override(&fake_cargo, &log, &override_config)?;
+        assert_doctest_record(&record, SHELL_SENSITIVE_RUSTDOC_FLAGS, source)?;
+    }
+    Ok(())
+}
+
+#[cfg(unix)]
+proptest! {
+    #![proptest_config(ProptestConfig::with_cases(16))]
+
+    #[test]
+    fn property_doctest_preserves_rustdoc_override_values(
+        rustdoc_flags in rustdoc_flags_strategy(),
+    ) {
+        let temporary = tempdir().expect("create fake Cargo directory");
+        let log = temporary.path().join("cargo-environment.log");
+        let fake_cargo = write_fake_cargo(temporary.path()).expect("write fake Cargo executable");
+
+        for (source, command_line) in [("environment", false), ("command line", true)] {
+            let override_config = RustdocOverride {
+                rustdoc_flags: &rustdoc_flags,
+                source,
+                command_line,
+            };
+            let record = run_doctest_with_override(
+                &fake_cargo,
+                &log,
+                &override_config,
+            )
+            .expect("run doctest through fake Cargo");
+            assert_doctest_record(&record, &rustdoc_flags, source)
+                .expect("preserve the Rustdoc override in Cargo's environment");
+        }
+    }
+}