diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b7f1146..073e3f7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,6 +30,18 @@ jobs:
           fi
           echo "clean"
 
+      - name: Fail if a crate root lacks #![forbid(unsafe_code)]
+        run: |
+          set -euo pipefail
+          status=0
+          while IFS= read -r root; do
+            if ! grep -q '^#!\[forbid(unsafe_code)\]' "$root"; then
+              echo "::error file=$root::crate root is missing #![forbid(unsafe_code)]"
+              status=1
+            fi
+          done < <(find . -path ./target -prune -o \( -path '*/src/lib.rs' -o -path '*/src/main.rs' -o -path '*/src/bin/*.rs' -o -name build.rs \) -print)
+          exit $status
+
   dependency-policy:
     name: Dependency licenses & sources (cargo-deny)
     runs-on: ubuntu-latest
diff --git a/fasterhenry-cli/build.rs b/fasterhenry-cli/build.rs
index 6d0dafd..34852fa 100644
--- a/fasterhenry-cli/build.rs
+++ b/fasterhenry-cli/build.rs
@@ -1,6 +1,8 @@
 // Bakes the source revision into `--version` via FASTERHENRY_GIT_DESCRIBE.
 // Falls back to "unknown" where git is absent (a crates.io tarball build),
 // so the version string stays deterministic there.
+#![forbid(unsafe_code)]
+
 use std::process::Command;
 
 fn describe() -> String {
diff --git a/fasterhenry-cli/src/lib.rs b/fasterhenry-cli/src/lib.rs
index 4520474..1809f79 100644
--- a/fasterhenry-cli/src/lib.rs
+++ b/fasterhenry-cli/src/lib.rs
@@ -4,6 +4,8 @@
 //! The binary logic lives in this library so the tests can drive it without
 //! spawning a process; `src/main.rs` is a thin wrapper.
 
+#![forbid(unsafe_code)]
+
 pub mod cli;
 pub mod inp;
 pub mod mat;
diff --git a/fasterhenry-cli/src/main.rs b/fasterhenry-cli/src/main.rs
index be87555..6078b8b 100644
--- a/fasterhenry-cli/src/main.rs
+++ b/fasterhenry-cli/src/main.rs
@@ -5,6 +5,8 @@
 //! the explicit `fasterhenry run <deck.inp | problem.json>`, which writes
 //! one only when `--zc-mat` asks for it. See `--help`.
 
+#![forbid(unsafe_code)]
+
 use fasterhenry_cli::cli::{Invocation, RunArgs};
 use fasterhenry_cli::inp::ParseOptions;
 use fasterhenry_cli::spice::write_spice_subckt;