diff --git a/src/audita/corrections.py b/src/audita/corrections.py
index bdf6e8c..5fa6cab 100644
--- a/src/audita/corrections.py
+++ b/src/audita/corrections.py
@@ -1,10 +1,11 @@
 from dataclasses import asdict, dataclass
-from typing import Dict, Iterable, List, Literal, Optional, Tuple
+from typing import Callable, Dict, Iterable, List, Literal, Optional, Tuple
 
 from .errors import AuditaValidationError
 from .schemas import CorrectionCandidate, TranscriptSegment
 
 ReplacementMode = Literal["replace_all", "require_unique"]
+CorrectionGuard = Callable[[str, str], Optional[str]]
 
 
 @dataclass(frozen=True)
@@ -33,6 +34,7 @@ def apply_corrections(
     corrections: Iterable[CorrectionCandidate],
     confidence_threshold: float,
     replacement_mode: ReplacementMode = "replace_all",
+    correction_guard: Optional[CorrectionGuard] = None,
 ) -> CorrectionApplicationResult:
     if not 0.0 <= confidence_threshold <= 1.0:
         raise AuditaValidationError("Confidence threshold must be between 0.0 and 1.0.")
@@ -57,6 +59,11 @@ def apply_corrections(
         position = id_to_position[correction.id]
         segment = revised[position]
         revised_text = segment.text.replace(correction.original_text, correction.corrected_text)
+        if correction_guard is not None:
+            reason = correction_guard(segment.text, revised_text)
+            if reason is not None:
+                skipped.append(_skip(correction, reason, actual_text=segment.text))
+                continue
         revised[position] = segment.model_copy(update={"text": revised_text})
         applied_ids.append(correction.id)
 
diff --git a/src/audita/pipeline.py b/src/audita/pipeline.py
index 6665bb1..63a2565 100644
--- a/src/audita/pipeline.py
+++ b/src/audita/pipeline.py
@@ -8,10 +8,11 @@ from uuid import uuid4
 
 from .chunking import IndexedSegment, TranscriptSection, chunk_indexed_segments
 from .config import AuditaConfig
-from .corrections import ReplacementMode, SkippedCorrection, apply_corrections
+from .corrections import CorrectionGuard, ReplacementMode, SkippedCorrection, apply_corrections
 from .errors import AuditaError
 from .normalization import NormalizationResult, normalize_transcript
 from .passes import CorrectionPass, GlossaryCorrectionPass, GrammarCorrectionPass, LLMClient
+from .protection import ProtectedVocabulary
 from .schemas import Glossary, SourceTranscriptSegment, TranscriptSegment, parse_transcript_json
 
 
@@ -25,6 +26,7 @@ class StageSpec:
     max_llm_passes: int
     confidence_threshold: float
     replacement_mode: ReplacementMode
+    correction_guard: Optional[CorrectionGuard] = None
 
 
 def process_transcript(
@@ -64,6 +66,7 @@ def process_transcript(
             llm_client = InstructorLLMClient(config)
 
         working = list(normalization_result.transcript)
+        protected_vocabulary = ProtectedVocabulary.from_glossary(glossary)
         stages = [
             StageSpec(
                 name="glossary",
@@ -78,6 +81,7 @@ def process_transcript(
                 max_llm_passes=config.grammar_max_llm_passes,
                 confidence_threshold=config.grammar_confidence_threshold,
                 replacement_mode="require_unique",
+                correction_guard=protected_vocabulary.violation_reason,
             ),
         ]
         final_skipped: List[Tuple[str, SkippedCorrection]] = []
@@ -186,6 +190,7 @@ def _run_correction_stage(
             corrections,
             stage.confidence_threshold,
             replacement_mode=stage.replacement_mode,
+            correction_guard=stage.correction_guard,
         )
         working = application_result.transcript
 
diff --git a/src/audita/prompts.py b/src/audita/prompts.py
index bfff834..091edf8 100644
--- a/src/audita/prompts.py
+++ b/src/audita/prompts.py
@@ -88,7 +88,9 @@ def build_grammar_correction_messages(
         "- Allowed corrections are only capitalization changes, punctuation changes involving commas, periods, em dashes, and ellipses, homophone fixes, and spelling fixes.\n"
         "- Do not add, remove, reorder, or replace words except for clear homophone or spelling corrections that preserve the spoken content.\n"
         "- Do not paraphrase, summarize, clarify, smooth style, or change the speaker's intent or meaning.\n"
-        "- Treat the glossary as protected vocabulary and context; do not introduce new glossary substitutions during this grammar pass.\n"
+        "- Treat glossary names and aliases as protected spellings and context; do not introduce new glossary substitutions during this grammar pass.\n"
+        "- Do not autocorrect, Anglicize, replace, normalize, lowercase, or otherwise alter protected glossary names or aliases.\n"
+        "- Preserve canonical glossary capitalization for protected names and aliases, even if they look unusual.\n"
         "- Use the exact id from the input segment.\n"
         "- For returned corrections, original_text must be only the exact text span that needs replacement, not the full segment text unless the whole segment is the replacement span.\n"
         "- Choose an original_text span that appears exactly once in the current segment text.\n"
diff --git a/src/audita/protection.py b/src/audita/protection.py
new file mode 100644
index 0000000..3d8470e
--- /dev/null
+++ b/src/audita/protection.py
@@ -0,0 +1,63 @@
+import re
+from dataclasses import dataclass
+from typing import Dict, List, Optional, Pattern
+
+from .schemas import Glossary
+
+
+@dataclass(frozen=True)
+class ProtectedVocabulary:
+    canonical_by_folded: Dict[str, str]
+    pattern: Optional[Pattern[str]]
+
+    @classmethod
+    def from_glossary(cls, glossary: Glossary) -> "ProtectedVocabulary":
+        canonical_by_folded: Dict[str, str] = {}
+        for entry in glossary.glossary:
+            _add_term(canonical_by_folded, entry.name)
+            for alias in entry.aliases:
+                _add_term(canonical_by_folded, alias)
+
+        terms = list(canonical_by_folded.values())
+        if not terms:
+            return cls(canonical_by_folded=canonical_by_folded, pattern=None)
+
+        alternatives = sorted((re.escape(term) for term in terms), key=len, reverse=True)
+        pattern = re.compile(r"(?<!\w)(" + "|".join(alternatives) + r")(?!\w)", flags=re.IGNORECASE)
+        return cls(canonical_by_folded=canonical_by_folded, pattern=pattern)
+
+    def violation_reason(self, before: str, after: str) -> Optional[str]:
+        before_terms = self._terms(before)
+        after_terms = self._terms(after)
+        if len(before_terms) != len(after_terms):
+            return "grammar correction changes protected glossary term usage"
+
+        for before_term, after_term in zip(before_terms, after_terms):
+            if before_term.folded != after_term.folded:
+                return "grammar correction changes protected glossary term usage"
+            canonical = self.canonical_by_folded[after_term.folded]
+            if after_term.text != canonical:
+                return "grammar correction changes protected glossary term capitalization"
+
+        return None
+
+    def _terms(self, text: str) -> List["_ProtectedTerm"]:
+        if self.pattern is None:
+            return []
+        return [
+            _ProtectedTerm(text=match.group(0), folded=match.group(0).casefold())
+            for match in self.pattern.finditer(text)
+        ]
+
+
+@dataclass(frozen=True)
+class _ProtectedTerm:
+    text: str
+    folded: str
+
+
+def _add_term(canonical_by_folded: Dict[str, str], term: str) -> None:
+    stripped = term.strip()
+    if not stripped:
+        return
+    canonical_by_folded.setdefault(stripped.casefold(), stripped)
diff --git a/tests/test_config.py b/tests/test_config.py
index 3273bfd..511424d 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -33,7 +33,6 @@ def test_config_uses_defaults_with_api_key():
     assert config.normalize_max_segment_gap == DEFAULT_NORMALIZE_MAX_SEGMENT_GAP
     assert config.normalize_max_segment_gap == 5.0
     assert config.normalize_ellipsis_gap == DEFAULT_NORMALIZE_ELLIPSIS_GAP
-    assert config.normalize_ellipsis_gap == 2.0
     assert config.normalize_max_segment_duration == DEFAULT_NORMALIZE_MAX_SEGMENT_DURATION
     assert config.normalize_max_segment_duration == 60.0
     assert config.normalize_max_segment_tokens == DEFAULT_NORMALIZE_MAX_SEGMENT_TOKENS
diff --git a/tests/test_corrections.py b/tests/test_corrections.py
index ee05c23..c064609 100644
--- a/tests/test_corrections.py
+++ b/tests/test_corrections.py
@@ -171,6 +171,56 @@ def test_apply_corrections_requires_unique_match_when_configured():
     assert "more than once" in result.skipped[0].reason
 
 
+def test_apply_corrections_skips_when_guard_rejects_replacement():
+    transcript = parse_transcript_json(
+        """
+        [
+          {"id": 1, "speaker": "Eric", "start": 0.0, "end": 1.0, "text": "Hrank moves."}
+        ]
+        """
+    )
+    correction = CorrectionCandidate(
+        id=1,
+        original_text="Hrank",
+        corrected_text="Frank",
+        confidence=0.8,
+    )
+
+    result = apply_corrections(
+        transcript,
+        [correction],
+        confidence_threshold=0.8,
+        replacement_mode="require_unique",
+        correction_guard=lambda before, after: "protected term changed" if before != after else None,
+    )
+
+    assert result.transcript[0].text == "Hrank moves."
+    assert len(result.skipped) == 1
+    assert result.skipped[0].reason == "protected term changed"
+    assert result.skipped[0].actual_text == "Hrank moves."
+
+
+def test_apply_corrections_without_guard_remains_permissive():
+    transcript = parse_transcript_json(
+        """
+        [
+          {"id": 1, "speaker": "Eric", "start": 0.0, "end": 1.0, "text": "Frank moves."}
+        ]
+        """
+    )
+    correction = CorrectionCandidate(
+        id=1,
+        original_text="Frank",
+        corrected_text="Hrank",
+        confidence=0.8,
+    )
+
+    result = apply_corrections(transcript, [correction], confidence_threshold=0.8)
+
+    assert result.transcript[0].text == "Hrank moves."
+    assert result.skipped == []
+
+
 def test_apply_corrections_skips_empty_original_text():
     transcript = _transcript()
     correction = CorrectionCandidate(
diff --git a/tests/test_pipeline.py b/tests/test_pipeline.py
index bcd3a20..2080e3f 100644
--- a/tests/test_pipeline.py
+++ b/tests/test_pipeline.py
@@ -305,6 +305,59 @@ def test_grammar_stage_runs_after_glossary_and_sees_corrected_text(tmp_path):
     assert revised[0].text == "I ask Chauntea."
 
 
+def test_grammar_stage_cannot_reverse_glossary_protected_term(tmp_path):
+    transcript = parse_source_transcript_json(
+        """
+        [
+          {"speaker": "Eric", "start": 0.0, "end": 1.0, "text": "Frank moves."}
+        ]
+        """
+    )
+    glossary = parse_glossary_yaml(
+        """
+        glossary:
+          - name: "Hrank"
+            category: pc
+            summary: "Hrank is a player character."
+        """
+    )
+    glossary_correction = CorrectionCandidate(
+        id=1,
+        original_text="Frank",
+        corrected_text="Hrank",
+        confidence=0.95,
+    )
+    grammar_reversal = CorrectionCandidate(
+        id=1,
+        original_text="Hrank",
+        corrected_text="Frank",
+        confidence=0.95,
+    )
+    fake_client = FakeLLMClient(
+        [
+            CorrectionSet(corrections=[glossary_correction]),
+            CorrectionSet(corrections=[grammar_reversal]),
+        ]
+    )
+    progress = []
+
+    revised = process_transcript(
+        transcript,
+        glossary,
+        _config(tmp_path, grammar_max_llm_passes=1),
+        llm_client=fake_client,
+        progress=progress.append,
+    )
+
+    assert revised[0].text == "Hrank moves."
+    assert any("Skipping grammar correction for id 1" in message for message in progress)
+    run_dirs = list((tmp_path / "work").iterdir())
+    assert len(run_dirs) == 1
+    diagnostics = json.loads((run_dirs[0] / "skipped-corrections.json").read_text(encoding="utf-8"))
+    assert diagnostics["skipped_corrections"][0]["stage"] == "grammar"
+    assert "protected glossary term" in diagnostics["skipped_corrections"][0]["reason"]
+
+
 def test_grammar_stage_retries_repeated_span_and_applies_unique_retry(tmp_path):
     transcript = parse_source_transcript_json(
         """
diff --git a/tests/test_prompts.py b/tests/test_prompts.py
index 1e2bd4e..a712d79 100644
--- a/tests/test_prompts.py
+++ b/tests/test_prompts.py
@@ -93,7 +93,9 @@ def test_grammar_prompt_limits_readability_corrections_and_protects_glossary():
     assert "homophone fixes" in prompt_text
     assert "spelling fixes" in prompt_text
     assert "Do not paraphrase" in prompt_text
-    assert "protected vocabulary" in prompt_text
+    assert "glossary names and aliases as protected spellings" in prompt_text
+    assert "Do not autocorrect, Anglicize, replace, normalize, lowercase" in prompt_text
+    assert "Preserve canonical glossary capitalization" in prompt_text
     assert "appears exactly once" in prompt_text
     assert "Do not return speaker, start, or end fields" in prompt_text
 
diff --git a/tests/test_protection.py b/tests/test_protection.py
new file mode 100644
index 0000000..74825cc
--- /dev/null
+++ b/tests/test_protection.py
@@ -0,0 +1,52 @@
+from audita.protection import ProtectedVocabulary
+from audita.schemas import parse_glossary_yaml
+
+
+def _vocabulary():
+    glossary = parse_glossary_yaml(
+        """
+        glossary:
+          - name: "Hrank"
+            aliases:
+              - "Greenfield"
+            category: pc
+            summary: "Hrank Greenfield is a player character."
+        """
+    )
+    return ProtectedVocabulary.from_glossary(glossary)
+
+
+def test_protection_blocks_replacing_protected_term():
+    vocabulary = _vocabulary()
+
+    assert vocabulary.violation_reason("Hrank moves.", "Frank moves.") is not None
+
+
+def test_protection_blocks_lowercasing_protected_term():
+    vocabulary = _vocabulary()
+
+    assert vocabulary.violation_reason("Hrank moves.", "hrank moves.") is not None
+
+
+def test_protection_allows_canonical_capitalization():
+    vocabulary = _vocabulary()
+
+    assert vocabulary.violation_reason("hrank moves.", "Hrank moves.") is None
+
+
+def test_protection_allows_punctuation_around_protected_term():
+    vocabulary = _vocabulary()
+
+    assert vocabulary.violation_reason("Hrank, moves.", "Hrank. Moves.") is None
+
+
+def test_protection_does_not_match_terms_inside_larger_words():
+    vocabulary = _vocabulary()
+
+    assert vocabulary.violation_reason("The shrank spell worked.", "The shrank spell works.") is None
+
+
+def test_protection_applies_to_aliases():
+    vocabulary = _vocabulary()
+
+    assert vocabulary.violation_reason("Greenfield waits.", "greenfield waits.") is not None