diff --git a/src/executors/semgrep.yml b/src/executors/semgrep.yml
index 734de7f..494a13b 100644
--- a/src/executors/semgrep.yml
+++ b/src/executors/semgrep.yml
@@ -3,8 +3,8 @@ description: >
 parameters:
   version:
     type: string
-    default: "1.61.1"
+    default: "1.181.0"
     description: Semgrep image version tag.
 docker:
-  - image: returntocorp/semgrep:<< parameters.version >>
+  - image: semgrep/semgrep:<< parameters.version >>
 resource_class: medium
diff --git a/src/scripts/run_semgrep.sh b/src/scripts/run_semgrep.sh
index 80cc365..8ae1aee 100755
--- a/src/scripts/run_semgrep.sh
+++ b/src/scripts/run_semgrep.sh
@@ -15,22 +15,45 @@ munitor_header "run_semgrep"
 
 CONFIG="${SEMGREP_CONFIG:-auto}"
 FAIL_ON_FINDINGS="${SEMGREP_FAIL_ON_FINDINGS:-true}"
+REPORT="${SEMGREP_REPORT:-/tmp/semgrep-results.json}"
 
 echo "Running Semgrep SAST scan (config: ${CONFIG}, fail_on_findings: ${FAIL_ON_FINDINGS})..."
 
+EXIT_CODE=0
 semgrep ci \
   --config "${CONFIG}" \
   --json \
-  --output /tmp/semgrep-results.json || {
-    EXIT_CODE=$?
-    if [[ "${FAIL_ON_FINDINGS}" == "true" ]]; then
-      echo "ERROR: Semgrep found issues."
-      echo "Review the report at: /tmp/semgrep-results.json"
-      exit "${EXIT_CODE}"
-    else
-      echo "WARNING: Semgrep found issues (warn-only mode, not failing build)."
-      echo "Review the report at: /tmp/semgrep-results.json"
-    fi
-  }
+  --output "${REPORT}" || EXIT_CODE=$?
+
+# Summarise the report, and fail a scan that ran no rules or scanned no files:
+# semgrep exits 0 when the downloaded rules fail to parse (an outdated semgrep),
+# which used to pass this job without scanning anything.
+python3 - "${REPORT}" <<'PY'
+import json, sys
+report = json.load(open(sys.argv[1]))
+scanned = len(report.get("paths", {}).get("scanned", []))
+results = report.get("results", [])
+errors = report.get("errors", [])
+rule_errors = [e for e in errors if "rule" in str(e.get("type", "")).lower()
+               or "config" in str(e.get("message", "")).lower()]
+print(f"Semgrep: {scanned} files scanned, {len(results)} findings, {len(errors)} errors.")
+for r in results[:50]:
+    print(f"  {r.get('check_id')}  {r.get('path')}:{r.get('start', {}).get('line')}")
+if scanned == 0 or rule_errors:
+    for e in rule_errors[:5]:
+        print(f"  error: {str(e.get('message', e))[:300]}")
+    print("ERROR: Semgrep did not run its rules (no files scanned or invalid rule configuration).")
+    sys.exit(2)
+PY
+
+if [[ "${EXIT_CODE}" -ne 0 ]]; then
+  if [[ "${FAIL_ON_FINDINGS}" == "true" ]]; then
+    echo "ERROR: Semgrep found issues."
+    echo "Review the report at: ${REPORT}"
+    exit "${EXIT_CODE}"
+  fi
+  echo "WARNING: Semgrep found issues (warn-only mode, not failing build)."
+  echo "Review the report at: ${REPORT}"
+fi
 
 echo "Semgrep scan completed."
diff --git a/src/scripts/run_trivy.sh b/src/scripts/run_trivy.sh
index c9bcffd..3063c1b 100755
--- a/src/scripts/run_trivy.sh
+++ b/src/scripts/run_trivy.sh
@@ -36,13 +36,17 @@ fi
 
 echo "Running Trivy filesystem scan..."
 
+# --exit-code 1: without it trivy exits 0 even when it reports HIGH/CRITICAL
+# findings, so this job could never fail.
 trivy fs \
   --format json \
   --output /tmp/trivy-results.json \
   --severity HIGH,CRITICAL \
+  --exit-code 1 \
   . || {
     EXIT_CODE=$?
     echo "Trivy found vulnerabilities. See /tmp/trivy-results.json"
+    trivy fs --severity HIGH,CRITICAL . || true
     exit "${EXIT_CODE}"
   }
 
diff --git a/tests/test_scan_gates.sh b/tests/test_scan_gates.sh
new file mode 100644
index 0000000..95d99d9
--- /dev/null
+++ b/tests/test_scan_gates.sh
@@ -0,0 +1,93 @@
+#!/usr/bin/env bash
+# The filesystem Trivy scan and the Semgrep scan must fail when they find
+# something, and Semgrep must fail when it ran no rules. Local tool stubs; no
+# network needed.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+SRC_SCRIPTS="$(cd "${SCRIPT_DIR}/../src/scripts" && pwd)"
+WORK=$(mktemp -d)
+trap 'rm -rf "${WORK}"' EXIT
+PASS=0
+FAIL=0
+pass() { echo "PASS"; PASS=$((PASS + 1)); }
+fail() { echo "FAIL"; FAIL=$((FAIL + 1)); }
+
+mkdir -p "${WORK}/home/bin" "${WORK}/bin" "${WORK}/repo"
+cat > "${WORK}/home/bin/trivy" <<'EOF'
+#!/usr/bin/env bash
+printf 'trivy %s\n' "$*" >> "${CALL_LOG}"
+# Real trivy exits 0 on findings unless --exit-code is given.
+for a in "$@"; do [[ "$a" == --exit-code ]] && exit "${SCAN_EXIT:-0}"; done
+exit 0
+EOF
+cat > "${WORK}/bin/semgrep" <<'EOF'
+#!/usr/bin/env bash
+printf '%s\n' "${SEMGREP_FAKE_REPORT}" > "${SEMGREP_REPORT}"
+exit "${SEMGREP_FAKE_EXIT:-0}"
+EOF
+chmod +x "${WORK}/home/bin/trivy" "${WORK}/bin/semgrep"
+export PATH="${WORK}/bin:${PATH}" HOME="${WORK}/home" CALL_LOG="${WORK}/calls"
+export SEMGREP_REPORT="${WORK}/semgrep.json"
+cd "${WORK}/repo"
+
+echo "=== Scan gate tests ==="
+echo -n "  TEST: trivy fs fails the job on HIGH/CRITICAL findings... "
+if ! SCAN_EXIT=1 bash "${SRC_SCRIPTS}/run_trivy.sh" > "${WORK}/trivy.log" 2>&1 &&
+  grep -q '^trivy fs .*--severity HIGH,CRITICAL --exit-code 1 ' "${CALL_LOG}"; then
+  pass
+else
+  fail
+fi
+
+echo -n "  TEST: trivy fs passes a clean scan... "
+if SCAN_EXIT=0 bash "${SRC_SCRIPTS}/run_trivy.sh" > "${WORK}/trivy.log" 2>&1; then
+  pass
+else
+  fail
+fi
+
+if command -v python3 &>/dev/null; then
+  CLEAN='{"results":[],"errors":[],"paths":{"scanned":["a.java","b.java"]}}'
+  FOUND='{"results":[{"check_id":"java.lang.security.x","path":"a.java","start":{"line":3}}],"errors":[],"paths":{"scanned":["a.java"]}}'
+  NORULES='{"results":[],"errors":[{"type":"InvalidRuleSchemaError","message":"invalid configuration file found (1 configs were invalid)"}],"paths":{"scanned":[]}}'
+
+  echo -n "  TEST: semgrep passes a clean scan... "
+  if SEMGREP_FAKE_REPORT="${CLEAN}" bash "${SRC_SCRIPTS}/run_semgrep.sh" > "${WORK}/sg.log" 2>&1 &&
+    grep -q '2 files scanned, 0 findings' "${WORK}/sg.log"; then
+    pass
+  else
+    fail
+  fi
+
+  echo -n "  TEST: semgrep fails on findings and lists them... "
+  if ! SEMGREP_FAKE_REPORT="${FOUND}" SEMGREP_FAKE_EXIT=1 bash "${SRC_SCRIPTS}/run_semgrep.sh" > "${WORK}/sg.log" 2>&1 &&
+    grep -q 'java.lang.security.x  a.java:3' "${WORK}/sg.log"; then
+    pass
+  else
+    fail
+  fi
+
+  echo -n "  TEST: semgrep warn-only mode passes with findings... "
+  if SEMGREP_FAIL_ON_FINDINGS=false SEMGREP_FAKE_REPORT="${FOUND}" SEMGREP_FAKE_EXIT=1 \
+    bash "${SRC_SCRIPTS}/run_semgrep.sh" > "${WORK}/sg.log" 2>&1; then
+    pass
+  else
+    fail
+  fi
+
+  echo -n "  TEST: semgrep fails when no rules ran, even with exit 0 and warn-only... "
+  if ! SEMGREP_FAIL_ON_FINDINGS=false SEMGREP_FAKE_REPORT="${NORULES}" SEMGREP_FAKE_EXIT=0 \
+    bash "${SRC_SCRIPTS}/run_semgrep.sh" > "${WORK}/sg.log" 2>&1 &&
+    grep -q 'did not run its rules' "${WORK}/sg.log"; then
+    pass
+  else
+    fail
+  fi
+else
+  echo "  SKIP: semgrep gate tests need python3"
+fi
+
+echo ""
+echo "Results: ${PASS} passed, ${FAIL} failed"
+[[ "${FAIL}" -eq 0 ]]