diff --git a/build/build-jasp.sh b/build/build-jasp.sh
index be400d0..25d611b 100755
--- a/build/build-jasp.sh
+++ b/build/build-jasp.sh
@@ -381,6 +381,34 @@ for module in "${ALL_MODULES[@]}"; do
   fi
 done
 
+# Modules are built from their default branch, which upstream occasionally
+# leaves broken: jaspDescriptives master carried a stray "|" in renv.lock from
+# 2026-10-07, which stopped the lockfile patch below and the whole build. A
+# module whose lockfile does not parse falls back to its newest release tag that
+# is no newer than the JASP release; with no such tag the build stops here.
+for module in "${ALL_MODULES[@]}"; do
+  dir="ModuleBundleBuildDir/Modules/${module}"
+  [[ -f "$dir/renv.lock" ]] || continue
+  python3 -c 'import json, sys; json.load(open(sys.argv[1]))' "$dir/renv.lock" 2>/dev/null && continue
+  fallback="$(git ls-remote --tags --refs "https://github.com/jasp-stats/${module}" 'v*' \
+    | sed 's|.*refs/tags/||' | python3 -c '
+import re, sys
+key = lambda t: [int(n) for n in re.findall(r"\d+", t)]
+limit = key(sys.argv[1])
+tags = [t for t in sys.stdin.read().split() if re.fullmatch(r"v[\d.]+", t) and key(t) <= limit]
+print(max(tags, key=key) if tags else "")
+' "$JASP_TAG")"
+  if [[ -z "$fallback" ]]; then
+    echo "error: ${module}/renv.lock on the default branch is not valid JSON" >&2
+    echo "       and the module has no release tag up to ${JASP_TAG} to fall back to" >&2
+    exit 1
+  fi
+  log "${module}: renv.lock on the default branch does not parse, building ${fallback} instead"
+  rm -rf "$dir"
+  git clone --depth 1 --branch "$fallback" "https://github.com/jasp-stats/${module}" "$dir"
+  python3 -c 'import json, sys; json.load(open(sys.argv[1]))' "$dir/renv.lock"
+done
+
 # This has to run after the modules are cloned: it once ran before, found no
 # lockfiles, patched nothing, and every module then failed on later 1.4.6.
 #