diff --git a/crates/fidc-core/src/platform_expr_strategy.rs b/crates/fidc-core/src/platform_expr_strategy.rs
index 3d2eab0..9e73179 100644
--- a/crates/fidc-core/src/platform_expr_strategy.rs
+++ b/crates/fidc-core/src/platform_expr_strategy.rs
@@ -2993,26 +2993,33 @@ impl PlatformExprStrategy {
     }
 
     fn rewrite_ternary(expr: &str) -> String {
-        let Some((question_idx, colon_idx)) = Self::find_top_level_ternary(expr) else {
-            return expr.trim().to_string();
+        let trimmed = expr.trim();
+        let Some((condition_start, question_idx, colon_idx, false_end)) =
+            Self::find_ternary_span(trimmed)
+        else {
+            return trimmed.to_string();
         };
-        let condition = Self::rewrite_ternary(expr[..question_idx].trim());
-        let when_true = Self::rewrite_ternary(expr[question_idx + 1..colon_idx].trim());
-        let when_false = Self::rewrite_ternary(expr[colon_idx + 1..].trim());
-        format!(
-            "if {} {{ {} }} else {{ {} }}",
+        let condition = Self::rewrite_ternary(trimmed[condition_start..question_idx].trim());
+        let when_true = Self::rewrite_ternary(trimmed[question_idx + 1..colon_idx].trim());
+        let when_false = Self::rewrite_ternary(trimmed[colon_idx + 1..false_end].trim());
+        let mut rewritten = String::new();
+        rewritten.push_str(&trimmed[..condition_start]);
+        rewritten.push_str(&format!(
+            "(if {} {{ {} }} else {{ {} }})",
             condition, when_true, when_false
-        )
+        ));
+        rewritten.push_str(&trimmed[false_end..]);
+        Self::rewrite_ternary(&rewritten)
     }
 
-    fn find_top_level_ternary(expr: &str) -> Option<(usize, usize)> {
+    fn find_ternary_span(expr: &str) -> Option<(usize, usize, usize, usize)> {
         let mut paren_depth = 0i32;
         let mut brace_depth = 0i32;
         let mut bracket_depth = 0i32;
         let mut in_single_quote = false;
         let mut in_double_quote = false;
         let mut escaped = false;
-        let mut question_stack = Vec::new();
+        let mut question_stack: Vec<(usize, i32, i32, i32)> = Vec::new();
 
         for (idx, ch) in expr.char_indices() {
             if escaped {
@@ -3036,13 +3043,25 @@ impl PlatformExprStrategy {
                 '}' => brace_depth -= 1,
                 '[' => bracket_depth += 1,
                 ']' => bracket_depth -= 1,
-                '?' if paren_depth == 0 && brace_depth == 0 && bracket_depth == 0 => {
-                    question_stack.push(idx);
+                '?' => {
+                    question_stack.push((idx, paren_depth, brace_depth, bracket_depth));
                 }
-                ':' if paren_depth == 0 && brace_depth == 0 && bracket_depth == 0 => {
-                    if let Some(question_idx) = question_stack.pop() {
-                        if question_stack.is_empty() {
-                            return Some((question_idx, idx));
+                ':' => {
+                    if let Some(&(question_idx, question_paren, question_brace, question_bracket)) =
+                        question_stack.last()
+                    {
+                        if question_paren == paren_depth
+                            && question_brace == brace_depth
+                            && question_bracket == bracket_depth
+                        {
+                            question_stack.pop();
+                            let condition_start = Self::find_ternary_condition_start(
+                                expr,
+                                question_idx,
+                                question_paren,
+                            );
+                            let false_end = Self::find_ternary_false_end(expr, idx, paren_depth);
+                            return Some((condition_start, question_idx, idx, false_end));
                         }
                     }
                 }
@@ -3052,6 +3071,97 @@ impl PlatformExprStrategy {
         None
     }
 
+    fn find_ternary_condition_start(
+        expr: &str,
+        question_idx: usize,
+        ternary_paren_depth: i32,
+    ) -> usize {
+        let mut paren_depth = 0i32;
+        let mut brace_depth = 0i32;
+        let mut bracket_depth = 0i32;
+        let mut in_single_quote = false;
+        let mut in_double_quote = false;
+        let mut escaped = false;
+        let mut start = 0usize;
+
+        for (idx, ch) in expr.char_indices() {
+            if idx >= question_idx {
+                break;
+            }
+            if escaped {
+                escaped = false;
+                continue;
+            }
+            match ch {
+                '\\' if in_single_quote || in_double_quote => escaped = true,
+                '\'' if !in_double_quote => in_single_quote = !in_single_quote,
+                '"' if !in_single_quote => in_double_quote = !in_double_quote,
+                _ if in_single_quote || in_double_quote => {}
+                '(' => {
+                    let next_depth = paren_depth + 1;
+                    paren_depth += 1;
+                    if next_depth == ternary_paren_depth && brace_depth == 0 && bracket_depth == 0
+                    {
+                        start = idx + ch.len_utf8();
+                    }
+                }
+                ')' => paren_depth -= 1,
+                '{' => brace_depth += 1,
+                '}' => brace_depth -= 1,
+                '[' => bracket_depth += 1,
+                ']' => bracket_depth -= 1,
+                ',' if paren_depth == 0 && brace_depth == 0 && bracket_depth == 0 => {
+                    start = idx + ch.len_utf8();
+                }
+                _ => {}
+            }
+        }
+        start
+    }
+
+    fn find_ternary_false_end(expr: &str, colon_idx: usize, ternary_paren_depth: i32) -> usize {
+        let mut paren_depth = ternary_paren_depth;
+        let mut brace_depth = 0i32;
+        let mut bracket_depth = 0i32;
+        let mut in_single_quote = false;
+        let mut in_double_quote = false;
+        let mut escaped = false;
+
+        for (idx, ch) in expr[colon_idx + 1..].char_indices() {
+            let absolute_idx = colon_idx + 1 + idx;
+            if escaped {
+                escaped = false;
+                continue;
+            }
+            match ch {
+                '\\' if in_single_quote || in_double_quote => escaped = true,
+                '\'' if !in_double_quote => in_single_quote = !in_single_quote,
+                '"' if !in_single_quote => in_double_quote = !in_double_quote,
+                _ if in_single_quote || in_double_quote => {}
+                '(' => paren_depth += 1,
+                ')' => {
+                    if paren_depth == ternary_paren_depth && brace_depth == 0 && bracket_depth == 0
+                    {
+                        return absolute_idx;
+                    }
+                    paren_depth -= 1;
+                }
+                '{' => brace_depth += 1,
+                '}' => brace_depth -= 1,
+                '[' => bracket_depth += 1,
+                ']' => bracket_depth -= 1,
+                ',' if paren_depth == ternary_paren_depth
+                    && brace_depth == 0
+                    && bracket_depth == 0 =>
+                {
+                    return absolute_idx;
+                }
+                _ => {}
+            }
+        }
+        expr.len()
+    }
+
     fn eval_float(
         &self,
         ctx: &StrategyContext<'_>,
@@ -4720,6 +4830,14 @@ mod tests {
         NaiveDate::from_ymd_opt(year, month, day).expect("valid date")
     }
 
+    #[test]
+    fn platform_expr_rewrites_nested_ternary() {
+        let expr = "pct_change(\"close\", 10) + (((close / rolling_mean(\"close\", 20)) - 1) > 0 ? 0.04 : -0.04)";
+        let rewritten = PlatformExprStrategy::rewrite_ternary(expr);
+        assert!(rewritten.contains("if ((close / rolling_mean(\"close\", 20)) - 1) > 0"));
+        assert!(!rewritten.contains('?'));
+    }
+
     fn sample_calendar() -> TradingCalendar {
         TradingCalendar::new(vec![
             d(2025, 1, 30),