diff --git a/crates/fidc-core/src/data.rs b/crates/fidc-core/src/data.rs
index cf978ae..de3a361 100644
--- a/crates/fidc-core/src/data.rs
+++ b/crates/fidc-core/src/data.rs
@@ -4403,6 +4403,16 @@ fn normalize_factor_snapshots(
                     }
                 })
                 .collect();
+            if snapshot
+                .extra_factors
+                .contains_key(BACKWARD_ADJUSTMENT_FACTOR_FIELD)
+            {
+                return Err(DataSetError::ReservedTypedFactorInExtraMap {
+                    date: snapshot.date,
+                    symbol: snapshot.symbol,
+                    field: BACKWARD_ADJUSTMENT_FACTOR_FIELD,
+                });
+            }
             Ok(snapshot)
         })
         .collect()
@@ -6349,6 +6359,21 @@ mod tests {
             normalize_factor_snapshots(vec![snapshot(Some(0.0), BTreeMap::new())]),
             Err(DataSetError::InvalidBackwardAdjustmentFactor { .. })
         ));
+        for field in [
+            " ADJUSTMENT_FACTOR_BACKWARD1 ",
+            "\"adjustment_factor_backward1\"",
+            "'adjustment_factor_backward1'",
+        ] {
+            for typed_value in [None, Some(1.0)] {
+                assert!(matches!(
+                    normalize_factor_snapshots(vec![snapshot(
+                        typed_value,
+                        BTreeMap::from([(Cow::Borrowed(field), 2.0)]),
+                    )]),
+                    Err(DataSetError::ReservedTypedFactorInExtraMap { .. })
+                ), "reserved alias accepted: {field}");
+            }
+        }
     }
 
     #[test]