diff --git a/include/mruby.h b/include/mruby.h
index ea750635a..b9dc7a917 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -157,17 +157,6 @@ typedef uint32_t mrb_aspec;
 typedef struct mrb_irep mrb_irep;
 struct mrb_state;
 
-/**
- * Function pointer type of custom allocator used in @see mrb_open_allocf.
- *
- * The function pointing it must behave similarly as realloc except:
- * - If ptr is NULL it must allocate new space.
- * - If size is zero, ptr must be freed.
- *
- * See mrb_basic_alloc_func in src/allocf.c for the default implementation.
- */
-typedef void* (*mrb_allocf) (void *ptr, size_t size);
-
 #ifndef MRB_FIXED_STATE_ATEXIT_STACK_SIZE
 #define MRB_FIXED_STATE_ATEXIT_STACK_SIZE 5
 #endif
@@ -1237,19 +1226,6 @@ MRB_API char* mrb_locale_from_utf8(const char *p, int len);
  */
 MRB_API mrb_state* mrb_open(void);
 
-/**
- * Create new mrb_state with custom allocators.
- *
- * @param f
- *      Reference to the allocation function.
- * @param ud
- *      User data will be passed to custom allocator f.
- *      If user data isn't required just pass NULL.
- * @return
- *      Pointer to the newly created mrb_state.
- */
-MRB_API mrb_state* mrb_open_allocf(mrb_allocf f, void *ud);
-
 /**
  * Create new mrb_state with just the mruby core
  *
@@ -1262,7 +1238,7 @@ MRB_API mrb_state* mrb_open_allocf(mrb_allocf f, void *ud);
  * @return
  *      Pointer to the newly created mrb_state.
  */
-MRB_API mrb_state* mrb_open_core(mrb_allocf f, void *ud);
+MRB_API mrb_state* mrb_open_core(void);
 
 /**
  * Closes and frees a mrb_state.
diff --git a/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c b/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c
index 550ebc0c7..a7ab67509 100644
--- a/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c
+++ b/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c
@@ -286,7 +286,7 @@ dump_file(mrb_state *mrb, FILE *wfp, const char *outfile, const struct RProc *pr
 int
 main(int argc, char **argv)
 {
-  mrb_state *mrb = mrb_open_core(NULL, NULL);
+  mrb_state *mrb = mrb_open_core();
   int n, result;
   struct mrbc_args args;
   FILE *wfp;
diff --git a/mrbgems/mruby-bin-strip/tools/mruby-strip/mruby-strip.c b/mrbgems/mruby-bin-strip/tools/mruby-strip/mruby-strip.c
index 47009ee0c..172ba313f 100644
--- a/mrbgems/mruby-bin-strip/tools/mruby-strip/mruby-strip.c
+++ b/mrbgems/mruby-bin-strip/tools/mruby-strip/mruby-strip.c
@@ -126,7 +126,7 @@ main(int argc, char **argv)
     print_usage(argv[0]);
     return EXIT_FAILURE;
   }
-  mrb = mrb_open_core(mrb_basic_alloc_func, NULL);
+  mrb = mrb_open_core();
   if (mrb == NULL) {
     fputs("Invalid mrb_state, exiting mruby-strip\n", stderr);
     return EXIT_FAILURE;
diff --git a/mrbgems/mruby-test/mrbgem.rake b/mrbgems/mruby-test/mrbgem.rake
index ac78fc811..d8339fec0 100644
--- a/mrbgems/mruby-test/mrbgem.rake
+++ b/mrbgems/mruby-test/mrbgem.rake
@@ -69,7 +69,7 @@ MRuby::Gem::Specification.new('mruby-test') do |spec|
           unless g.test_args.empty?
             f.puts %Q[  mrb_value test_args_hash;]
           end
-          f.puts %Q[  mrb_state *mrb2 = mrb_open_core(mrb_basic_alloc_func, NULL);]
+          f.puts %Q[  mrb_state *mrb2 = mrb_open_core();]
           f.puts %Q[  if (mrb2 == NULL) {]
           f.puts %Q[    fprintf(stderr, "Invalid mrb_state, exiting \%s", __func__);]
           f.puts %Q[    exit(EXIT_FAILURE);]
diff --git a/src/state.c b/src/state.c
index 1b92487cf..f94f108be 100644
--- a/src/state.c
+++ b/src/state.c
@@ -36,13 +36,12 @@ init_gc_and_core(mrb_state *mrb, void *opaque)
 }
 
 MRB_API mrb_state*
-mrb_open_core(mrb_allocf f, void *ud)
+mrb_open_core(void)
 {
   static const mrb_state mrb_state_zero = { 0 };
   mrb_state *mrb;
 
-  if (f == NULL) f = mrb_basic_alloc_func;
-  mrb = (mrb_state*)(f)(NULL, sizeof(mrb_state));
+  mrb = (mrb_state*)mrb_basic_alloc_func(NULL, sizeof(mrb_state));
   if (mrb == NULL) return NULL;
 
   *mrb = mrb_state_zero;
@@ -56,14 +55,6 @@ mrb_open_core(mrb_allocf f, void *ud)
   return mrb;
 }
 
-MRB_API mrb_state*
-mrb_open(void)
-{
-  mrb_state *mrb = mrb_open_allocf(mrb_basic_alloc_func, NULL);
-
-  return mrb;
-}
-
 #ifndef MRB_NO_GEMS
 static void
 init_mrbgems(mrb_state *mrb, void *opaque)
@@ -73,9 +64,9 @@ init_mrbgems(mrb_state *mrb, void *opaque)
 #endif
 
 MRB_API mrb_state*
-mrb_open_allocf(mrb_allocf f, void *ud)
+mrb_open(void)
 {
-  mrb_state *mrb = mrb_open_core(f, ud);
+  mrb_state *mrb = mrb_open_core();
 
   if (mrb == NULL) {
     return NULL;