diff --git a/bootstraptest/test_yjit.rb b/bootstraptest/test_yjit.rb
index bd44f3ac3e..fc592520e8 100644
--- a/bootstraptest/test_yjit.rb
+++ b/bootstraptest/test_yjit.rb
@@ -5416,3 +5416,22 @@ assert_equal 'foo', %{
 
   10.times.map { foo.dup }.last
 }
+
+# regression test for [Bug #21772]
+# local variable type tracking desync
+assert_normal_exit %q{
+  def some_method = 0
+
+  def test_body(key)
+    some_method
+    key = key.to_s # setting of local relevant
+
+    key == "symbol"
+  end
+
+  def jit_caller = test_body("session_id")
+
+  jit_caller # first iteration, non-escaped environment
+  alias some_method binding # induce environment escape
+  test_body(:symbol)
+}
diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index 865f80ca4f..4a53e8834c 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -2518,6 +2518,7 @@ fn gen_setlocal_generic(
     ep_offset: u32,
     level: u32,
 ) -> Option<CodegenStatus> {
+    // Post condition: The type of of the set local is updated in the Context.
     let value_type = asm.ctx.get_opnd_type(StackOpnd(0));
 
     // Fallback because of write barrier
@@ -2539,6 +2540,11 @@ fn gen_setlocal_generic(
         );
         asm.stack_pop(1);
 
+        // Set local type in the context
+        if level == 0 {
+            let local_idx = ep_offset_to_local_idx(jit.get_iseq(), ep_offset).as_usize();
+            asm.ctx.set_local_type(local_idx, value_type);
+        }
         return Some(KeepCompiling);
     }
 
@@ -2591,6 +2597,7 @@ fn gen_setlocal_generic(
         );
     }
 
+    // Set local type in the context
     if level == 0 {
         let local_idx = ep_offset_to_local_idx(jit.get_iseq(), ep_offset).as_usize();
         asm.ctx.set_local_type(local_idx, value_type);