diff --git a/src/mir/builder/rewrite/known.rs b/src/mir/builder/rewrite/known.rs
index 0c5d3eed..9f98aaa1 100644
--- a/src/mir/builder/rewrite/known.rs
+++ b/src/mir/builder/rewrite/known.rs
@@ -53,18 +53,20 @@ pub(crate) fn try_known_rewrite(
         return None;
     }
 
-    // Phase 287 P4: Don't rewrite for primitive types
+    // Phase 287 P4: Don't rewrite for primitive types (toString/stringify/str only)
     // (should use universal slot toString[#0], not user-defined static methods)
-    if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
-        use crate::mir::MirType;
-        match recv_type {
-            MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
-                if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
-                    eprintln!("[P287-GUARD] try_known_rewrite: BLOCKED primitive type {:?}", recv_type);
+    if method == "toString" || method == "stringify" || method == "str" {
+        if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
+            use crate::mir::MirType;
+            match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
+                    if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
+                        eprintln!("[P287-GUARD] try_known_rewrite: BLOCKED primitive type {:?} for {}", recv_type, method);
+                    }
+                    return None;
                 }
-                return None;
+                _ => {}
             }
-            _ => {}
         }
     }
 
@@ -144,18 +146,20 @@ pub(crate) fn try_known_rewrite_to_dst(
         return None;
     }
 
-    // Phase 287 P4: Don't rewrite for primitive types
+    // Phase 287 P4: Don't rewrite for primitive types (toString/stringify/str only)
     // (should use universal slot toString[#0], not user-defined static methods)
-    if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
-        use crate::mir::MirType;
-        match recv_type {
-            MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
-                if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
-                    eprintln!("[P287-GUARD] try_known_rewrite_to_dst: BLOCKED primitive type {:?}", recv_type);
+    if method == "toString" || method == "stringify" || method == "str" {
+        if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
+            use crate::mir::MirType;
+            match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
+                    if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
+                        eprintln!("[P287-GUARD] try_known_rewrite_to_dst: BLOCKED primitive type {:?} for {}", recv_type, method);
+                    }
+                    return None;
                 }
-                return None;
+                _ => {}
             }
-            _ => {}
         }
     }
 
@@ -240,18 +244,20 @@ pub(crate) fn try_unique_suffix_rewrite(
         return None;
     }
 
-    // Phase 287 P4: Don't rewrite for primitive types
+    // Phase 287 P4: Don't rewrite for primitive types (toString/stringify/str only)
     // (should use universal slot toString[#0], not user-defined static methods)
-    if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
-        use crate::mir::MirType;
-        match recv_type {
-            MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
-                if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
-                    eprintln!("[P287-GUARD] try_unique_suffix_rewrite: BLOCKED primitive type {:?}", recv_type);
+    if method == "toString" || method == "stringify" || method == "str" {
+        if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
+            use crate::mir::MirType;
+            match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
+                    if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
+                        eprintln!("[P287-GUARD] try_unique_suffix_rewrite: BLOCKED primitive type {:?} for {}", recv_type, method);
+                    }
+                    return None;
                 }
-                return None;
+                _ => {}
             }
-            _ => {}
         }
     }
 
@@ -312,18 +318,20 @@ pub(crate) fn try_unique_suffix_rewrite_to_dst(
         return None;
     }
 
-    // Phase 287 P4: Don't rewrite for primitive types
+    // Phase 287 P4: Don't rewrite for primitive types (toString/stringify/str only)
     // (should use universal slot toString[#0], not user-defined static methods)
-    if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
-        use crate::mir::MirType;
-        match recv_type {
-            MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
-                if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
-                    eprintln!("[P287-GUARD] try_unique_suffix_rewrite_to_dst: BLOCKED primitive type {:?}", recv_type);
+    if method == "toString" || method == "stringify" || method == "str" {
+        if let Some(recv_type) = builder.type_ctx.value_types.get(&object_value) {
+            use crate::mir::MirType;
+            match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => {
+                    if std::env::var("NYASH_STATIC_CALL_TRACE").ok().as_deref() == Some("1") {
+                        eprintln!("[P287-GUARD] try_unique_suffix_rewrite_to_dst: BLOCKED primitive type {:?} for {}", recv_type, method);
+                    }
+                    return None;
                 }
-                return None;
+                _ => {}
             }
-            _ => {}
         }
     }