diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7876211..c939166 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,6 +15,20 @@ concurrency:
   cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
+  credit-guard:
+    name: Changelog and contributor credit (issue #113)
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+      - name: Check CHANGELOG.md and CONTRIBUTORS.md updates
+        env:
+          PR_AUTHOR: ${{ github.event.pull_request.user.login }}
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: bash scripts/check_credit.sh "$BASE_SHA" "$HEAD_SHA" "$PR_AUTHOR"
   lint:
     name: Lint and type check
     runs-on: ubuntu-latest
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2b4a735..2258e26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ Format: [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
 
 ## [Unreleased]
 
+### Added
+- `credit-guard` CI job: pull requests touching `philanthropy/` must also
+  update this changelog, and the author must be credited in
+  CONTRIBUTORS.md. Implemented as `scripts/check_credit.sh`, wired into
+  `ci.yml` on `pull_request` events only; failures surface as inline
+  `::error::` annotations on the Files tab. Closes #113.
 ### Fixed
 - `CRMCleaner.transform` no longer silently corrupts complex amounts into
   wrong finite floats: cells holding actual `complex` values are masked to
diff --git a/scripts/check_credit.sh b/scripts/check_credit.sh
new file mode 100755
index 0000000..2a72d33
--- /dev/null
+++ b/scripts/check_credit.sh
@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Credit guard (issue #113): a PR that changes code under philanthropy/ must
+# also touch CHANGELOG.md, and its author must already be credited in
+# CONTRIBUTORS.md. Runs on pull_request events only; direct pushes to main
+# and history that predates the guard are not checked.
+set -euo pipefail
+
+base=$1
+head=$2
+author=${3:-}
+
+changed=$(git diff --name-only "$base" "$head")
+
+if ! echo "$changed" | grep -q '^philanthropy/'; then
+  echo "credit guard: no source changes under philanthropy/ - nothing to check"
+  exit 0
+fi
+
+if ! echo "$changed" | grep -qx 'CHANGELOG.md'; then
+  echo "::error::This PR touches files under philanthropy/ but not CHANGELOG.md. Add a line under [Unreleased] describing the change."
+  exit 1
+fi
+
+if [ -z "$author" ]; then
+  echo "::error::PR author could not be determined; cannot run the CONTRIBUTORS.md check."
+  exit 1
+fi
+
+# Match the literal token "@<author>" not followed by another login character.
+# The author is interpolated literally (awk index, no regex), so bot logins
+# such as dependabot[bot] are not misread as a character class.
+if ! awk -v token="@$author" '
+  index($0, token) {
+    rest = substr($0, index($0, token) + length(token))
+    if (rest == "" || rest !~ /^[A-Za-z0-9_-]/) { found = 1; exit }
+  }
+  END { exit found ? 0 : 1 }
+' CONTRIBUTORS.md; then
+  echo "::error::This PR touches files under philanthropy/ but its author (@$author) is not listed in CONTRIBUTORS.md. Add yourself in the same pull request (see 'Getting listed')."
+  exit 1
+fi
+
+echo "credit guard OK: changelog touched and @$author is credited"