diff --git a/codex/wiki.py b/codex/wiki.py
index 7a0ec8b..59e17df 100644
--- a/codex/wiki.py
+++ b/codex/wiki.py
@@ -186,8 +186,15 @@ def _retrieve_chunks(
         ).fetchall()
 
     # Filter reference-list chunks: skip chunks whose content looks like a bibliography
-    # (heuristic: > 60 % of lines match "^\[\d+\]" or "^[A-Z][a-z]+,?\s+[A-Z]\.").
-    ref_pattern = re.compile(r"^\s*(\[\d+\]|[A-Z][a-z]+,?\s+[A-Z]\.)", re.MULTILINE)
+    # (heuristic: > 60 % of lines look like "[12]" refs or "Surname, I." authors).
+    # The author alternative excludes common math-structure words ("Theorem A.",
+    # "Lemma B.") so theorem-dense chunks aren't mistaken for a reference list (R-2).
+    ref_pattern = re.compile(
+        r"^\s*(\[\d+\]|(?!(?:Theorem|Lemma|Proposition|Corollary|Definition|Proof|"
+        r"Section|Figure|Fig|Table|Equation|Eq|Remark|Example|Chapter)\b)"
+        r"[A-Z][a-z]+,?\s+[A-Z]\.)",
+        re.MULTILINE,
+    )
     filtered: list[dict[str, Any]] = []
     for row in rows:
         content: str = row["content"]
@@ -336,8 +343,9 @@ def _run_grounding_guard(
     for chunk in chunks:
         bk = str(chunk.get("bibkey") or "")
         if bk:
-            # Content words of the chunk (stopwords removed, lowercased)
-            cw = " ".join(_content_words(chunk["content"]))
+            # Content words of the chunk, space-padded so a 5-gram match is bounded
+            # by whole tokens, not a substring bleeding across words (audit C-6).
+            cw = " " + " ".join(_content_words(chunk["content"])) + " "
             bib_index.setdefault(bk, []).append(cw)
 
     for claim in claims:
@@ -359,7 +367,7 @@ def _run_grounding_guard(
 
         found = False
         for i in range(len(content) - 4):  # content-5-grams
-            gram = " ".join(content[i : i + 5])
+            gram = " " + " ".join(content[i : i + 5]) + " "  # padded: token-boundary match
             if any(gram in src for src in sources):
                 found = True
                 break
diff --git a/tests/wiki/test_compile.py b/tests/wiki/test_compile.py
index c0db957..8afcd5b 100644
--- a/tests/wiki/test_compile.py
+++ b/tests/wiki/test_compile.py
@@ -230,6 +230,30 @@ def test_grounding_guard_robust_to_trailing_comma() -> None:
     assert result[0].grounded is True
 
 
+def test_grounding_guard_no_substring_bleed_across_tokens() -> None:
+    """A 5-gram must match whole tokens, not bleed into a longer chunk word (audit C-6).
+
+    The chunk contains 'subset'; a claim whose first token is 'set' must NOT ground
+    by substring-matching the suffix of 'subset'.
+    """
+    chunks = [
+        {
+            "id": 99,
+            "paper_id": "p",
+            "ord": 0,
+            "bibkey": "TestBib",
+            "content": "the subset conformal map energy functional is minimized here",
+        }
+    ]
+    claim = Claim(
+        text="the set conformal map energy functional",
+        bibkey="TestBib",
+        locator="chunk 0",
+    )
+    result = _run_grounding_guard([claim], chunks)
+    assert result[0].grounded is False
+
+
 # ---------------------------------------------------------------------------
 # _inject_cross_refs
 # ---------------------------------------------------------------------------