diff --git a/load.c b/load.c
index 28c17e8b9c..4fb13017a5 100644
--- a/load.c
+++ b/load.c
@@ -152,6 +152,12 @@ get_loaded_features(void)
     return GET_VM()->loaded_features;
 }
 
+static VALUE
+get_loaded_features_realpaths(void)
+{
+    return GET_VM()->loaded_features_realpaths;
+}
+
 static VALUE
 get_LOADED_FEATURES(ID _x, VALUE *_y)
 {
@@ -317,6 +323,9 @@ get_loaded_features_index(void)
 	/* The sharing was broken; something (other than us in rb_provide_feature())
 	   modified loaded_features.  Rebuild the index. */
 	st_foreach(vm->loaded_features_index, loaded_features_index_clear_i, 0);
+
+        VALUE realpaths = vm->loaded_features_realpaths;
+        rb_hash_clear(realpaths);
 	features = vm->loaded_features;
 	for (i = 0; i < RARRAY_LEN(features); i++) {
 	    VALUE entry, as_str;
@@ -328,6 +337,15 @@ get_loaded_features_index(void)
 	    features_index_add(as_str, INT2FIX(i));
 	}
 	reset_loaded_features_snapshot();
+
+        features = rb_ary_dup(vm->loaded_features_snapshot);
+        long j = RARRAY_LEN(features);
+        for (i = 0; i < j; i++) {
+            VALUE as_str = rb_ary_entry(features, i);
+            VALUE realpath = rb_check_realpath(Qnil, as_str, NULL);
+            if (NIL_P(realpath)) realpath = as_str;
+            rb_hash_aset(realpaths, rb_fstring(realpath), Qtrue);
+        }
     }
     return vm->loaded_features_index;
 }
@@ -1063,6 +1081,8 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception)
     char *volatile ftptr = 0;
     VALUE path;
     volatile VALUE saved_path;
+    VALUE realpath = 0;
+    VALUE realpaths = get_loaded_features_realpaths();
     volatile bool reset_ext_config = false;
     struct rb_ext_config prev_ext_config;
 
@@ -1090,6 +1110,10 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception)
 	    else if (!*ftptr) {
 		result = TAG_RETURN;
 	    }
+            else if (RTEST(rb_hash_aref(realpaths,
+                                        realpath = rb_realpath_internal(Qnil, path, 1)))) {
+                result = 0;
+            }
 	    else {
 		switch (found) {
 		  case 'r':
@@ -1141,7 +1165,12 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception)
         rb_exc_raise(ec->errinfo);
     }
 
-    if (result == TAG_RETURN) rb_provide_feature(path);
+    if (result == TAG_RETURN) {
+        rb_provide_feature(path);
+        if (realpath) {
+            rb_hash_aset(realpaths, rb_fstring(realpath), Qtrue);
+        }
+    }
     ec->errinfo = saved.errinfo;
 
     RUBY_DTRACE_HOOK(REQUIRE_RETURN, RSTRING_PTR(fname));
@@ -1341,6 +1370,8 @@ Init_load(void)
     vm->loaded_features = rb_ary_new();
     vm->loaded_features_snapshot = rb_ary_tmp_new(0);
     vm->loaded_features_index = st_init_numtable();
+    vm->loaded_features_realpaths = rb_hash_new();
+    rb_obj_hide(vm->loaded_features_realpaths);
 
     rb_define_global_function("load", rb_f_load, -1);
     rb_define_global_function("require", rb_f_require, 1);
diff --git a/test/ruby/test_require.rb b/test/ruby/test_require.rb
index 401b274ef6..e996c6d641 100644
--- a/test/ruby/test_require.rb
+++ b/test/ruby/test_require.rb
@@ -434,6 +434,32 @@ class TestRequire < Test::Unit::TestCase
     }
   end
 
+  def test_relative_symlink_realpath
+    Dir.mktmpdir {|tmp|
+      Dir.chdir(tmp) {
+        Dir.mkdir "a"
+        File.open("a/a.rb", "w") {|f| f.puts 'require_relative "b"' }
+        File.open("a/b.rb", "w") {|f| f.puts '$t += 1' }
+        Dir.mkdir "b"
+        File.binwrite("c.rb", <<~RUBY)
+          $t = 0
+          $:.unshift(File.expand_path('../b', __FILE__))
+          require "b"
+          require "a"
+          print $t
+        RUBY
+        begin
+          File.symlink("../a/a.rb", "b/a.rb")
+          File.symlink("../a/b.rb", "b/b.rb")
+          result = IO.popen([EnvUtil.rubybin, "c.rb"], &:read)
+          assert_equal("1", result, "bug17885 [ruby-core:104010]")
+        rescue NotImplementedError, Errno::EACCES
+          skip "File.symlink is not implemented"
+        end
+      }
+    }
+  end
+
   def test_frozen_loaded_features
     bug3756 = '[ruby-core:31913]'
     assert_in_out_err(['-e', '$LOADED_FEATURES.freeze; require "ostruct"'], "",
@@ -711,8 +737,8 @@ class TestRequire < Test::Unit::TestCase
       assert_in_out_err([{"RUBYOPT" => nil}, "-", script.path], "#{<<~"begin;"}\n#{<<~"end;"}", %w(:ok), [], bug7530, timeout: 60)
       begin;
         PATH = ARGV.shift
-        THREADS = 4
-        ITERATIONS_PER_THREAD = 1000
+        THREADS = 30
+        ITERATIONS_PER_THREAD = 300
 
         THREADS.times.map {
           Thread.new do
diff --git a/vm.c b/vm.c
index 1a21638978..f6b0f94690 100644
--- a/vm.c
+++ b/vm.c
@@ -2486,6 +2486,7 @@ rb_vm_update_references(void *ptr)
         vm->expanded_load_path = rb_gc_location(vm->expanded_load_path);
         vm->loaded_features = rb_gc_location(vm->loaded_features);
         vm->loaded_features_snapshot = rb_gc_location(vm->loaded_features_snapshot);
+        vm->loaded_features_realpaths = rb_gc_location(vm->loaded_features_realpaths);
         vm->top_self = rb_gc_location(vm->top_self);
         vm->orig_progname = rb_gc_location(vm->orig_progname);
 
@@ -2573,6 +2574,7 @@ rb_vm_mark(void *ptr)
         rb_gc_mark_movable(vm->expanded_load_path);
         rb_gc_mark_movable(vm->loaded_features);
         rb_gc_mark_movable(vm->loaded_features_snapshot);
+        rb_gc_mark_movable(vm->loaded_features_realpaths);
         rb_gc_mark_movable(vm->top_self);
         rb_gc_mark_movable(vm->orig_progname);
         RUBY_MARK_MOVABLE_UNLESS_NULL(vm->coverages);
diff --git a/vm_core.h b/vm_core.h
index 58243b133e..6b627f4a82 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -631,6 +631,7 @@ typedef struct rb_vm_struct {
     VALUE expanded_load_path;
     VALUE loaded_features;
     VALUE loaded_features_snapshot;
+    VALUE loaded_features_realpaths;
     struct st_table *loaded_features_index;
     struct st_table *loading_table;