diff --git a/error.c b/error.c
index b898183..93e5e7c 100644
--- a/error.c
+++ b/error.c
@@ -1597,6 +1597,7 @@ rb_mod_sys_fail(VALUE mod, const char *mesg)
 {
     VALUE exc = make_errno_exc(mesg);
     rb_extend_object(exc, mod);
+    FL_SET(CLASS_OF(exc), RCLASS_EPHEMERAL);
     rb_exc_raise(exc);
 }
 
@@ -1605,6 +1606,7 @@ rb_mod_syserr_fail(VALUE mod, int e, const char *mesg)
 {
     VALUE exc = rb_syserr_new(e, mesg);
     rb_extend_object(exc, mod);
+    FL_SET(CLASS_OF(exc), RCLASS_EPHEMERAL);
     rb_exc_raise(exc);
 }
 
diff --git a/ext/openssl/ossl_ssl.c b/ext/openssl/ossl_ssl.c
index 3122c0e..5c197d1 100644
--- a/ext/openssl/ossl_ssl.c
+++ b/ext/openssl/ossl_ssl.c
@@ -1076,6 +1076,7 @@ write_would_block(int nonblock)
     if (nonblock) {
         VALUE exc = ossl_exc_new(eSSLError, "write would block");
         rb_extend_object(exc, rb_mWaitWritable);
+        FL_SET(CLASS_OF(exc), RCLASS_EPHEMERAL);
         rb_exc_raise(exc);
     }
 }
@@ -1086,6 +1087,7 @@ read_would_block(int nonblock)
     if (nonblock) {
         VALUE exc = ossl_exc_new(eSSLError, "read would block");
         rb_extend_object(exc, rb_mWaitReadable);
+        FL_SET(CLASS_OF(exc), RCLASS_EPHEMERAL);
         rb_exc_raise(exc);
     }
 }
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index c8790df..143cd07 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -621,6 +621,7 @@ struct RClass {
     struct st_table *m_tbl;
     struct st_table *iv_index_tbl;
 };
+#define RCLASS_EPHEMERAL FL_USER1
 #define RCLASS_IV_TBL(c) (RCLASS(c)->ptr->iv_tbl)
 #define RCLASS_CONST_TBL(c) (RCLASS(c)->ptr->const_tbl)
 #define RCLASS_M_TBL(c) (RCLASS(c)->m_tbl)
diff --git a/vm_method.c b/vm_method.c
index 2087371..a771992 100644
--- a/vm_method.c
+++ b/vm_method.c
@@ -85,6 +85,10 @@ rb_clear_cache_by_class(VALUE klass)
 {
     struct cache_entry *ent, *end;
 
+    /* ephemeral class does not write to cache */
+    if (FL_TEST(klass, RCLASS_EPHEMERAL))
+	return;
+
     rb_vm_change_state();
 
     if (!ruby_running)
@@ -417,8 +421,9 @@ rb_method_entry_get_without_cache(VALUE klass, ID id)
 {
     rb_method_entry_t *me = search_method(klass, id);
 
-    if (ruby_running) {
+    if (ruby_running && ! FL_TEST(klass, RCLASS_EPHEMERAL)) {
 	struct cache_entry *ent;
+
 	ent = cache + EXPR1(klass, id);
 	ent->klass = klass;