diff --git a/README.md b/README.md
index d1bfbcb..dfe9849 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,25 @@ netscaler-triage .\logs.7z
 
 Installation may require internet access. Analysis runs offline.
 
+### Update an existing installation
+
+Activate the same virtual environment used to run the tool, then run from the
+repository directory:
+
+```sh
+git pull
+python -m pip install --upgrade .
+netscaler-triage rules
+```
+
+For an environment managed by uv, use `uv sync --locked` after `git pull`.
+Version 1.0.1 fixes installation failures reporting `invalid perl operator: (?=`
+or `SigmaRegularExpressionError` when loading the bundled rules. pySigma 2 changed
+its default validation engine to RE2, which rejects lookaheads. The package now
+requires compatible pySigma 1.x; detection patterns and timed matching are
+unchanged. Reinstalling with the command above also downgrades an incompatible
+pySigma installation. Rerun any scan that stopped with this error.
+
 ## Everyday use
 
 ```sh
diff --git a/VALIDATION.txt b/VALIDATION.txt
index 2b338e4..ee93058 100644
--- a/VALIDATION.txt
+++ b/VALIDATION.txt
@@ -162,3 +162,18 @@ source mapping and validation results remain outside the public release.
 A subsequent presentation correction exposes original-file SHA-256 matches in
 SUMMARY.txt even without an event match. Three focused presentation tests passed,
 including this separate hash-only case; Ruff, formatting and strict mypy passed.
+
+DEPENDENCY COMPATIBILITY FIX — 2026-10-05
+
+Version 1.0.0 was installed in an isolated environment with pySigma 2.0.0.
+The bundled-rule validation reproduced the reported RE2 rejection of lookahead
+syntax. Version 1.0.1 constrains pySigma to >=1.5.1,<2, keeping the existing
+detection patterns and timeout-protected matching unchanged.
+
+Reinstalling the corrected package in that same environment automatically
+replaced pySigma 2.0.0 with 1.5.1. All 47 bundled Sigma rules validated, with
+246 explicit active indicators. All 138 tests passed against the installed
+package with Python warnings treated as errors. A new regression checks the
+reported lookahead pattern against raw and decoded text, including negative
+cases. Ruff lint, formatting and strict mypy across source and tests passed.
+This verification did not rerun the complete private forensic datasets.
diff --git a/pyproject.toml b/pyproject.toml
index 773ef6a..a9ffef0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "netscaler-triage"
-version = "1.0.0"
+version = "1.0.1"
 description = "Offline NetScaler evidence analysis with inspectable decoding and provenance"
 readme = "README.md"
 license = "MIT"
@@ -17,7 +17,8 @@ dependencies = [
     "rich>=14.1",
     "rich-argparse>=1.7",
     "pyzipper>=0.3.6",
-    "pysigma>=1.5.1",
+    # pySigma 2 defaults to RE2, which rejects the supported lookahead rules.
+    "pysigma>=1.5.1,<2",
 ]
 
 [project.scripts]
diff --git a/src/netscaler_triage/__init__.py b/src/netscaler_triage/__init__.py
index 3c4785b..f1f3945 100644
--- a/src/netscaler_triage/__init__.py
+++ b/src/netscaler_triage/__init__.py
@@ -1,3 +1,3 @@
 """Offline analysis; no discovered payload is ever executed."""
 
-__version__ = "1.0.0"
+__version__ = "1.0.1"
diff --git a/tests/test_sigma_rules.py b/tests/test_sigma_rules.py
index 31e94b4..e897fe1 100644
--- a/tests/test_sigma_rules.py
+++ b/tests/test_sigma_rules.py
@@ -13,6 +13,22 @@ def rule(detection: str, service: str = "") -> str:
 
 
 class SigmaTests(unittest.TestCase):
+    def test_lookahead_rule_on_raw_and_decoded_text(self) -> None:
+        matcher = SigmaMatcher.from_yaml(
+            rule(
+                "  s:\n"
+                "    raw|re: '(?im)^(?=.*(?:pitboss|NSPPE))"
+                "(?=.*(?:base64|PD9))(?=.*(?:2N|httpaccess))'\n"
+                "  condition: s\n"
+            )
+        )
+        sample = "pitboss NSPPE base64 httpaccess"
+        self.assertTrue(matcher.search({"raw": sample}))
+        hits = matcher.search_with_details({"raw": "encoded record"}, [sample])
+        self.assertEqual(hits[0]["basis"], ["decoded:0"])
+        for benign in ("pitboss NSPPE", "base64 httpaccess", "NSPPE base64"):
+            self.assertFalse(matcher.search({"raw": benign}))
+
     def test_catalog_not_repeated_in_hit(self) -> None:
         text = rule("  s: [abc]\n  condition: s\n")
         text += "indicators:\n  - type: ipv4\n    value: 192.0.2.1\n    status: reference_only\n"
diff --git a/uv.lock b/uv.lock
index 7925509..92286e7 100644
--- a/uv.lock
+++ b/uv.lock
@@ -546,7 +546,7 @@ wheels = [
 
 [[package]]
 name = "netscaler-triage"
-version = "1.0.0"
+version = "1.0.1"
 source = { editable = "." }
 dependencies = [
     { name = "py7zr" },
@@ -569,7 +569,7 @@ dev = [
 [package.metadata]
 requires-dist = [
     { name = "py7zr", specifier = ">=1.0" },
-    { name = "pysigma", specifier = ">=1.5.1" },
+    { name = "pysigma", specifier = ">=1.5.1,<2" },
     { name = "pyzipper", specifier = ">=0.3.6" },
     { name = "regex", specifier = ">=2025.11" },
     { name = "rich", specifier = ">=14.1" },