diff --git a/ChangeLog b/ChangeLog
index 9e49490574..cfd1268ece 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Apr 12 22:11:10 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* string.c (sym_to_proc), proc.c (rb_block_clear_env_self): clear
+	  caller's self which is useless, so that it can get collected.
+	  [Fixes GH-592]
+
 Sat Apr 12 09:26:48 2014  Eric Hodel  <drbrain@segment7.net>
 
 	* ext/openssl/ossl_ocsp.c:  [DOC] Document OpenSSL::OCSP.
diff --git a/internal.h b/internal.h
index 6c2951fa18..5890fdb959 100644
--- a/internal.h
+++ b/internal.h
@@ -758,6 +758,7 @@ ID rb_id_attrget(ID id);
 VALUE rb_proc_location(VALUE self);
 st_index_t rb_hash_proc(st_index_t hash, VALUE proc);
 int rb_block_arity(void);
+VALUE rb_block_clear_env_self(VALUE proc);
 
 /* process.c */
 #define RB_MAX_GROUPS (65536)
diff --git a/proc.c b/proc.c
index b36c7aa865..1271a3ba42 100644
--- a/proc.c
+++ b/proc.c
@@ -709,6 +709,17 @@ rb_block_lambda(void)
     return proc_new(rb_cProc, TRUE);
 }
 
+VALUE
+rb_block_clear_env_self(VALUE proc)
+{
+    rb_proc_t *po;
+    rb_env_t *env;
+    GetProcPtr(proc, po);
+    GetEnvPtr(po->envval, env);
+    env->env[0] = Qnil;
+    return proc;
+}
+
 VALUE
 rb_f_lambda(void)
 {
diff --git a/string.c b/string.c
index 56b27d9d75..28b1efa2e9 100644
--- a/string.c
+++ b/string.c
@@ -8506,6 +8506,7 @@ sym_to_proc(VALUE sym)
     }
     else {
 	proc = rb_proc_new(sym_call, (VALUE)id);
+	rb_block_clear_env_self(proc);
 	aryp[index] = sym;
 	aryp[index + 1] = proc;
 	return proc;