diff --git a/src/mir/builder/rewrite/known.rs b/src/mir/builder/rewrite/known.rs
index 9f98aaa1..8c21d707 100644
--- a/src/mir/builder/rewrite/known.rs
+++ b/src/mir/builder/rewrite/known.rs
@@ -58,14 +58,16 @@ pub(crate) fn try_known_rewrite(
     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;
+            let is_primitive = match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => true,
+                MirType::Box(name) if name == "IntegerBox" || name == "FloatBox" || name == "BoolBox" || name == "StringBox" => true,
+                _ => false,
+            };
+            if is_primitive {
+                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;
             }
         }
     }
@@ -151,14 +153,16 @@ pub(crate) fn try_known_rewrite_to_dst(
     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;
+            let is_primitive = match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => true,
+                MirType::Box(name) if name == "IntegerBox" || name == "FloatBox" || name == "BoolBox" || name == "StringBox" => true,
+                _ => false,
+            };
+            if is_primitive {
+                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;
             }
         }
     }
@@ -249,14 +253,16 @@ pub(crate) fn try_unique_suffix_rewrite(
     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;
+            let is_primitive = match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => true,
+                MirType::Box(name) if name == "IntegerBox" || name == "FloatBox" || name == "BoolBox" || name == "StringBox" => true,
+                _ => false,
+            };
+            if is_primitive {
+                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;
             }
         }
     }
@@ -323,14 +329,16 @@ pub(crate) fn try_unique_suffix_rewrite_to_dst(
     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") {
+            let is_primitive = match recv_type {
+                MirType::Integer | MirType::Float | MirType::Bool | MirType::String => true,
+                MirType::Box(name) if name == "IntegerBox" || name == "FloatBox" || name == "BoolBox" || name == "StringBox" => true,
+                _ => false,
+            };
+            if is_primitive {
+                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;
             }
         }
     }