diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 5156ed6453..b810366f0a 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -1982,12 +1982,14 @@ async fn run_turn(
     let mut base_instructions = turn_context.base_instructions.clone();
     if parallel_tool_calls {
         static INSTRUCTIONS: &str = include_str!("../templates/parallel/instructions.md");
-        static INSERTION_SPOT: &str = "## Editing constraints";
-        base_instructions
-            .as_mut()
-            .map(|base| base.replace(INSERTION_SPOT, INSTRUCTIONS));
+        if let Some(family) =
+            find_family_for_model(&sess.state.lock().await.session_configuration.model)
+        {
+            let mut new_instructions = base_instructions.unwrap_or(family.base_instructions);
+            new_instructions.push_str(INSTRUCTIONS);
+            base_instructions = Some(new_instructions);
+        }
     }
-
     let prompt = Prompt {
         input,
         tools: router.specs(),
diff --git a/codex-rs/core/templates/parallel/instructions.md b/codex-rs/core/templates/parallel/instructions.md
index d690501af7..292d585e45 100644
--- a/codex-rs/core/templates/parallel/instructions.md
+++ b/codex-rs/core/templates/parallel/instructions.md
@@ -1,3 +1,4 @@
+
 ## Exploration and reading files
 
 - **Think first.** Before any tool call, decide ALL files/resources you will need.
@@ -10,5 +11,3 @@
 * Always maximize parallelism. Never read files one-by-one unless logically unavoidable.
 * This concern every read/list/search operations including, but not only, `cat`, `rg`, `sed`, `ls`, `git show`, `nl`, `wc`, ...
 * Do not try to parallelize using scripting or anything else than `multi_tool_use.parallel`.
-
-## Editing constraints
\ No newline at end of file