diff --git a/bootstraptest/test_yjit.rb b/bootstraptest/test_yjit.rb
index f19629ec0e4e85..e9ce905e2c7073 100644
--- a/bootstraptest/test_yjit.rb
+++ b/bootstraptest/test_yjit.rb
@@ -5535,3 +5535,23 @@ def compiled_method
   # Resume the fiber — compiled_method's iseq must still be valid
   fiber.resume.to_s
 }
+
+# regression test for register mapping of methods with over 256 locals
+# [Bug #22074]
+assert_equal "ok", %q{
+  source = +"def many_locals\n"
+  source << "  total = 0\n"
+
+  128.times do |i|
+    source << "  y#{i} = 1\n"
+    source << "  x#{i} = Object.new\n"
+  end
+
+  source << "  total += 1\n"
+  source << "  raise total.inspect unless total == 1\n"
+  source << "end\n"
+
+  eval(source)
+  many_locals
+  "ok"
+}
diff --git a/yjit/src/backend/ir.rs b/yjit/src/backend/ir.rs
index 3fb67bc7cc1584..16a6ad49b357d4 100644
--- a/yjit/src/backend/ir.rs
+++ b/yjit/src/backend/ir.rs
@@ -242,7 +242,9 @@ impl Opnd
                     let last_idx = stack_size as i32 + VM_ENV_DATA_SIZE as i32 - 1;
                     assert!(last_idx <= idx, "Local index {} must be >= last local index {}", idx, last_idx);
                     assert!(idx <= last_idx + num_locals as i32, "Local index {} must be < last local index {} + local size {}", idx, last_idx, num_locals);
-                    RegOpnd::Local((last_idx + num_locals as i32 - idx) as u8)
+                    // Indices that don't fit in u8 are capped to u8::MAX, which is greater than MAX_CTX_LOCALS.
+                    let local_idx = last_idx + num_locals as i32 - idx;
+                    RegOpnd::Local(local_idx.try_into().unwrap_or(u8::MAX))
                 } else {
                     assert!(idx < stack_size as i32);
                     RegOpnd::Stack((stack_size as i32 - idx - 1) as u8)