diff --git a/.github/workflows/interface-sync.yml b/.github/workflows/interface-sync.yml
new file mode 100644
index 00000000..d074cec0
--- /dev/null
+++ b/.github/workflows/interface-sync.yml
@@ -0,0 +1,52 @@
+name: Interface Sync Guard
+
+permissions: {}
+
+# Guards the cross-language interface contract:
+#
+# The frontend SDK bundles generated Candid declarations (idlFactory + types)
+# that MUST stay in sync with the canister .did files. This job regenerates the
+# declarations from the committed .did using the pinned bindgen version and
+# fails if the result differs from what is checked in — i.e. someone changed a
+# .did but forgot to regenerate the frontend declarations (or edited the
+# generated files by hand).
+#
+# Note: the Rust <-> Motoko backend interface contract is already enforced
+# behaviorally — the Motoko canister is compiled to wasm and the Rust canister's
+# integration tests run against it (see backend/mo/canisters/*/Makefile and
+# backend-motoko.yml), so this guard deliberately focuses on the
+# frontend <-> canister seam, which is otherwise unguarded.
+
+on:
+  push:
+    branches:
+      - main
+      - master
+  pull_request:
+    paths:
+      - backend/rs/canisters/*/*.did
+      - frontend/ic_vetkeys/src/declarations/**
+      - frontend/ic_vetkeys/make_did_bindings.sh
+      - .github/workflows/interface-sync.yml
+
+jobs:
+  declarations-in-sync:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+        with:
+          persist-credentials: false
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+        with:
+          node-version: '22'
+      - name: Regenerate frontend declarations from committed .did files
+        working-directory: frontend/ic_vetkeys
+        run: SKIP_EXTRACT_CANDID=1 bash make_did_bindings.sh
+      - name: Fail if declarations are out of sync
+        run: |
+          set -eEuo pipefail
+          if ! git diff --exit-code -- frontend/ic_vetkeys/src/declarations; then
+            echo "::error::Frontend declarations are out of sync with the canister .did files."
+            echo "Run 'bash make_did_bindings.sh' in frontend/ic_vetkeys and commit the result."
+            exit 1
+          fi
diff --git a/frontend/ic_vetkeys/make_did_bindings.sh b/frontend/ic_vetkeys/make_did_bindings.sh
index efe3acbb..41d97b3b 100755
--- a/frontend/ic_vetkeys/make_did_bindings.sh
+++ b/frontend/ic_vetkeys/make_did_bindings.sh
@@ -1,17 +1,34 @@
 set -ex
 
+# Pin the bindgen version so regeneration is reproducible. The committed
+# declarations under src/declarations were generated with this version; the
+# interface-sync CI guard regenerates and diffs against them, so an unpinned
+# version (whatever `npx` resolves to) would cause spurious failures whenever a
+# newer bindgen ships cosmetic/formatting changes. Bump this deliberately and
+# commit the regenerated output together.
+BINDGEN_VERSION="0.3.0"
+
+# Set SKIP_EXTRACT_CANDID=1 to regenerate the TS declarations from the existing
+# committed .did files without rebuilding them from the Rust source. The
+# interface-sync CI guard uses this so the check stays reproducible (it depends
+# only on the pinned bindgen version and the committed .did, not on the
+# candid-extractor / wasm toolchain).
+SKIP_EXTRACT_CANDID="${SKIP_EXTRACT_CANDID:-0}"
+
 function make_and_copy_declarations () {
     DIR=$1
     NAME=$2
     DID_FILE=$3
 
-    pushd "$DIR/$NAME"
-    make extract-candid
-    popd
+    if [ "$SKIP_EXTRACT_CANDID" != "1" ]; then
+        pushd "$DIR/$NAME"
+        make extract-candid
+        popd
+    fi
 
     rm -rf "src/declarations/$NAME"
     mkdir -p "src/declarations/$NAME"
-    npx @icp-sdk/bindgen --did-file "$DIR/$NAME/$DID_FILE" --out-dir "src/declarations/$NAME" --declarations-flat --force
+    npx "@icp-sdk/bindgen@${BINDGEN_VERSION}" --did-file "$DIR/$NAME/$DID_FILE" --out-dir "src/declarations/$NAME" --declarations-flat --force
 }
 
 make_and_copy_declarations "../../backend/rs/canisters/" "ic_vetkeys_manager_canister" "ic_vetkeys_manager_canister.did"