diff --git a/internal/vm.h b/internal/vm.h
index 7fae590d19..09dfaf182e 100644
--- a/internal/vm.h
+++ b/internal/vm.h
@@ -69,6 +69,7 @@ const char *rb_type_str(enum ruby_value_type type);
 VALUE rb_check_funcall_default(VALUE, ID, int, const VALUE *, VALUE);
 VALUE rb_check_funcall_basic_kw(VALUE, ID, VALUE, int, const VALUE*, int);
 VALUE rb_yield_1(VALUE val);
+VALUE rb_ec_yield(struct rb_execution_context_struct *ec, VALUE val);
 VALUE rb_yield_force_blockarg(VALUE values);
 VALUE rb_lambda_call(VALUE obj, ID mid, int argc, const VALUE *argv,
                      rb_block_call_func_t bl_proc, int min_argc, int max_argc,
diff --git a/thread_sync.c b/thread_sync.c
index e54963a4fe..6af6aaddd6 100644
--- a/thread_sync.c
+++ b/thread_sync.c
@@ -650,7 +650,6 @@ rb_mutex_sleep(VALUE self, VALUE timeout)
     return rb_mut_sleep(GET_EC(), self, timeout);
 }
 
-
 VALUE
 rb_mutex_synchronize(VALUE self, VALUE (*func)(VALUE arg), VALUE arg)
 {
@@ -660,6 +659,12 @@ rb_mutex_synchronize(VALUE self, VALUE (*func)(VALUE arg), VALUE arg)
     return rb_ec_ensure(args.ec, func, arg, do_mutex_unlock_safe, (VALUE)&args);
 }
 
+static VALUE
+do_ec_yield(VALUE _ec)
+{
+    return rb_ec_yield((rb_execution_context_t *)_ec, Qundef);
+}
+
 VALUE
 rb_mut_synchronize(rb_execution_context_t *ec, VALUE self)
 {
@@ -669,7 +674,7 @@ rb_mut_synchronize(rb_execution_context_t *ec, VALUE self)
         .ec = ec,
     };
     do_mutex_lock(&args, 1);
-    return rb_ec_ensure(args.ec, rb_yield, Qundef, do_mutex_unlock_safe, (VALUE)&args);
+    return rb_ec_ensure(args.ec, do_ec_yield, (VALUE)ec, do_mutex_unlock_safe, (VALUE)&args);
 }
 
 void
diff --git a/vm_eval.c b/vm_eval.c
index 12bdabc330..34560d704a 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -1379,6 +1379,17 @@ rb_yield(VALUE val)
     }
 }
 
+VALUE
+rb_ec_yield(rb_execution_context_t *ec, VALUE val)
+{
+    if (UNDEF_P(val)) {
+        return vm_yield(ec, 0, NULL, RB_NO_KEYWORDS);
+    }
+    else {
+        return vm_yield(ec, 1, &val, RB_NO_KEYWORDS);
+    }
+}
+
 #undef rb_yield_values
 VALUE
 rb_yield_values(int n, ...)