diff --git a/crates/fidc-core/src/data.rs b/crates/fidc-core/src/data.rs
index d8bfb12..1ccf1cd 100644
--- a/crates/fidc-core/src/data.rs
+++ b/crates/fidc-core/src/data.rs
@@ -3311,6 +3311,16 @@ fn normalize_factor_snapshots(factors: Vec<DailyFactorSnapshot>) -> Vec<DailyFac
     factors
         .into_iter()
         .map(|mut snapshot| {
+            let already_normalized = snapshot.extra_factors.iter().all(|(field, value)| {
+                let trimmed = field.as_ref().trim().trim_matches('"').trim_matches('\'');
+                !trimmed.is_empty()
+                    && trimmed == field.as_ref()
+                    && trimmed.bytes().all(|byte| !byte.is_ascii_uppercase())
+                    && value.is_finite()
+            });
+            if already_normalized {
+                return snapshot;
+            }
             snapshot.extra_factors = snapshot
                 .extra_factors
                 .into_iter()
@@ -3970,6 +3980,41 @@ mod tests {
         assert_eq!(factor_numeric_value(&snapshot, "CUSTOM_FACTOR"), Some(3.5));
     }
 
+    #[test]
+    fn factor_snapshot_normalization_moves_clean_maps_and_repairs_dirty_maps() {
+        let date = NaiveDate::parse_from_str("2025-01-02", "%Y-%m-%d").unwrap();
+        let clean = normalize_factor_snapshots(vec![DailyFactorSnapshot {
+            date,
+            symbol: "000001.SZ".to_string(),
+            market_cap_bn: 1.0,
+            free_float_cap_bn: 1.0,
+            pe_ttm: 1.0,
+            turnover_ratio: None,
+            effective_turnover_ratio: None,
+            extra_factors: BTreeMap::from([(Cow::Borrowed("amount"), 10.0)]),
+        }]);
+        assert!(matches!(
+            clean[0].extra_factors.keys().next(),
+            Some(Cow::Borrowed("amount"))
+        ));
+
+        let dirty = normalize_factor_snapshots(vec![DailyFactorSnapshot {
+            date,
+            symbol: "000001.SZ".to_string(),
+            market_cap_bn: 1.0,
+            free_float_cap_bn: 1.0,
+            pe_ttm: 1.0,
+            turnover_ratio: None,
+            effective_turnover_ratio: None,
+            extra_factors: BTreeMap::from([
+                (Cow::Owned(" CUSTOM_FACTOR ".to_string()), 2.0),
+                (Cow::Borrowed("bad_nan"), f64::NAN),
+            ]),
+        }]);
+        assert_eq!(dirty[0].extra_factors.get("custom_factor"), Some(&2.0));
+        assert!(!dirty[0].extra_factors.contains_key("bad_nan"));
+    }
+
     #[test]
     fn symbol_price_series_test_constructor_sorts_unsorted_rows() {
         let series = SymbolPriceSeries::new(