diff --git a/bootstraptest/test_yjit.rb b/bootstraptest/test_yjit.rb
index 6b7d4839265d04..4d08ce70f18b07 100644
--- a/bootstraptest/test_yjit.rb
+++ b/bootstraptest/test_yjit.rb
@@ -4786,3 +4786,20 @@ def tests
 
   tests
 }
+
+# test String#stebyte with arguments that need conversion
+assert_equal "abc", %q{
+  str = +"a00"
+  def change_bytes(str, one, two)
+    str.setbyte(one, "b".ord)
+    str.setbyte(2, two)
+  end
+
+  to_int_1 = Object.new
+  to_int_99 = Object.new
+  def to_int_1.to_int = 1
+  def to_int_99.to_int = 99
+
+  change_bytes(str, to_int_1, to_int_99)
+  str
+}
diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index b047aa3310ae69..6233730c274cf5 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -5718,19 +5718,29 @@ fn jit_rb_str_getbyte(
 fn jit_rb_str_setbyte(
     jit: &mut JITState,
     asm: &mut Assembler,
-    _ocb: &mut OutlinedCb,
+    ocb: &mut OutlinedCb,
     _ci: *const rb_callinfo,
     cme: *const rb_callable_method_entry_t,
     _block: Option<BlockHandler>,
     _argc: i32,
     _known_recv_class: Option<VALUE>,
 ) -> bool {
+    // Check that arguments are fixnums since jit_prepare_lazy_frame_call()
+    // requires rb_str_setbyte() to be leaf or raise, but it tries to
+    // convert non-integer arguments by calling #to_int.
+    if !matches!(asm.ctx.two_fixnums_on_stack(jit), Some(true)) {
+        return false;
+    }
+
     // Raises when index is out of range. Lazily push a frame in that case.
     if !jit_prepare_lazy_frame_call(jit, asm, cme, StackOpnd(2)) {
         return false;
     }
     asm_comment!(asm, "String#setbyte");
 
+    // Check that arguments are fixnums
+    guard_two_fixnums(jit, asm, ocb);
+
     let value = asm.stack_opnd(0);
     let index = asm.stack_opnd(1);
     let recv = asm.stack_opnd(2);