diff --git a/include/mruby/proc.h b/include/mruby/proc.h
index 4c3db2a62..def00628f 100644
--- a/include/mruby/proc.h
+++ b/include/mruby/proc.h
@@ -136,12 +136,46 @@ MRB_API mrb_value mrb_proc_cfunc_env_get(mrb_state *mrb, mrb_int idx);
 
 MRB_API mrb_value mrb_load_proc(mrb_state *mrb, const struct RProc *proc);
 
+/**
+ *  It can be used to isolate top-level scopes referenced by blocks generated by
+ *  `mrb_load_string_cxt()` or similar called before entering the mruby VM (e.g. from `main()`).
+ *  In that case, the `ci` parameter should be `mrb->c->cibase`.
+ *
+ *      #include <mruby.h>
+ *      #include <mruby/compile.h>
+ *      #include <mruby/proc.h>
+ *
+ *      int
+ *      main(int argc, char **argv)
+ *      {
+ *        mrb_state *mrb;
+ *        mrbc_context *cxt;
+ *        mrb_value blk, ret;
+ *
+ *        mrb = mrb_open();
+ *        cxt = mrbc_context_new(mrb);
+ *        blk = mrb_load_string_cxt(mrb, "x, y, z = 1, 2, 3; proc { [x, y, z] }", cxt);
+ *        mrb_vm_ci_env_clear(mrb, mrb->c->cibase);
+ *        mrb_load_string_cxt(mrb, "x, y, z = 4, 5, 6", cxt);
+ *        ret = mrb_funcall(mrb, blk, "call", 0);
+ *        mrb_p(mrb, ret);  // => [1, 2, 3]
+ *                          // => [4, 5, 6] if `mrb_vm_ci_env_clear()` is commented out
+ *        mrbc_context_free(mrb, cxt);
+ *        mrb_close(mrb);
+ *
+ *        return 0;
+ *      }
+ *
+ *  The top-level local variable names stored in `mrbc_context` are retained.
+ *  Use also `mrbc_cleanup_local_variables()` at the same time, if necessary.
+ */
+MRB_API void mrb_vm_ci_env_clear(mrb_state *mrb, mrb_callinfo *ci);
+
 void mrb_vm_ci_proc_set(mrb_callinfo *ci, const struct RProc *p);
 struct RClass * mrb_vm_ci_target_class(const mrb_callinfo *ci);
 void mrb_vm_ci_target_class_set(mrb_callinfo *ci, struct RClass *tc);
 struct REnv * mrb_vm_ci_env(const mrb_callinfo *ci);
-MRB_API void mrb_vm_ci_env_clear(mrb_callinfo *ci);
-MRB_API void mrb_vm_ci_env_set(mrb_callinfo *ci, struct REnv *e);
+void mrb_vm_ci_env_set(mrb_callinfo *ci, struct REnv *e);
 
 MRB_END_DECL
 
diff --git a/lib/mruby/gem.rb b/lib/mruby/gem.rb
index 3ac952fcb..c04c2d44c 100644
--- a/lib/mruby/gem.rb
+++ b/lib/mruby/gem.rb
@@ -223,9 +223,7 @@ module MRuby
             f.puts %Q[    mrb_close(mrb);]
             f.puts %Q[    exit(EXIT_FAILURE);]
             f.puts %Q[  }]
-            f.puts %Q[  struct REnv *e = mrb_vm_ci_env(mrb->c->cibase);]
-            f.puts %Q[  mrb_vm_ci_env_clear(mrb->c->cibase);]
-            f.puts %Q[  mrb_env_unshare(mrb, e, FALSE);]
+            f.puts %Q[  mrb_vm_ci_env_clear(mrb, mrb->c->cibase);]
           end
           f.puts %Q[  mrb_gc_arena_restore(mrb, ai);]
           f.puts %Q[}]
diff --git a/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c b/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
index 78c3ed40f..8a723b12f 100644
--- a/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
+++ b/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c
@@ -508,7 +508,6 @@ main(int argc, char **argv)
 
   /* Load libraries */
   for (i = 0; i < args.libc; i++) {
-    struct REnv *e;
     FILE *lfp = fopen(args.libv[i], "r");
     if (lfp == NULL) {
       printf("Cannot open library file. (%s)\n", args.libv[i]);
@@ -517,9 +516,7 @@ main(int argc, char **argv)
     }
     mrb_load_file_cxt(mrb, lfp, cxt);
     fclose(lfp);
-    e = mrb_vm_ci_env(mrb->c->cibase);
-    mrb_vm_ci_env_set(mrb->c->cibase, NULL);
-    mrb_env_unshare(mrb, e, FALSE);
+    mrb_vm_ci_env_clear(mrb, mrb->c->cibase);
     mrbc_cleanup_local_variables(mrb, cxt);
   }
 
diff --git a/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c b/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c
index 3faaaccd3..966014dc1 100644
--- a/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c
+++ b/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c
@@ -326,7 +326,6 @@ main(int argc, char **argv)
 
     /* Load libraries */
     for (i = 0; i < args.libc; i++) {
-      struct REnv *e;
       FILE *lfp = fopen(args.libv[i], "rb");
       if (lfp == NULL) {
         fprintf(stderr, "%s: Cannot open library file: %s\n", *argv, args.libv[i]);
@@ -342,9 +341,7 @@ main(int argc, char **argv)
         v = mrb_load_detect_file_cxt(mrb, lfp, c);
       }
       fclose(lfp);
-      e = mrb_vm_ci_env(mrb->c->cibase);
-      mrb_vm_ci_env_set(mrb->c->cibase, NULL);
-      mrb_env_unshare(mrb, e, FALSE);
+      mrb_vm_ci_env_clear(mrb, mrb->c->cibase);
       mrbc_cleanup_local_variables(mrb, c);
     }
 
diff --git a/src/vm.c b/src/vm.c
index 2c72e35ab..f88ae6df5 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -318,22 +318,19 @@ ci_env_set(mrb_callinfo *ci, struct REnv *e)
   }
 }
 
-MRB_API void
+void
 mrb_vm_ci_env_set(mrb_callinfo *ci, struct REnv *e)
 {
   ci_env_set(ci, e);
 }
 
 MRB_API void
-mrb_vm_ci_env_clear(mrb_callinfo *ci)
+mrb_vm_ci_env_clear(mrb_state *mrb, mrb_callinfo *ci)
 {
-  if (ci->u.env) {
-    if (ci->u.env->tt == MRB_TT_ENV) {
-      ci->u.target_class = ci->u.env->c;
-    }
-  }
-  else {
-    ci->u.env = NULL;
+  struct REnv *e = ci->u.env;
+  if (e && e->tt == MRB_TT_ENV) {
+    ci->u.target_class = e->c;
+    mrb_env_unshare(mrb, e, FALSE);
   }
 }