diff --git a/load.c b/load.c
index f31b7aeaca961b..2ddeb11c8ea00d 100644
--- a/load.c
+++ b/load.c
@@ -944,6 +944,7 @@ rb_require_safe(VALUE fname, int safe)
 {
     volatile VALUE result = Qnil;
     rb_thread_t *th = GET_THREAD();
+    rb_vm_t *vm = GET_VM();
     volatile VALUE errinfo = th->errinfo;
     int state;
     struct {
@@ -951,6 +952,9 @@ rb_require_safe(VALUE fname, int safe)
     } volatile saved;
     char *volatile ftptr = 0;
 
+    if (strncmp(StringValuePtr(fname), "enumerator", 11) == 0)
+	return Qfalse;
+
     if (RUBY_DTRACE_REQUIRE_ENTRY_ENABLED()) {
 	RUBY_DTRACE_REQUIRE_ENTRY(StringValuePtr(fname),
 				  rb_sourcefile(),
@@ -960,9 +964,11 @@ rb_require_safe(VALUE fname, int safe)
     PUSH_TAG();
     saved.safe = rb_safe_level();
     if ((state = EXEC_TAG()) == 0) {
-	VALUE path;
+	VALUE ipath, path = 0;
 	long handle;
 	int found;
+	st_data_t key, val;
+	char *vals;
 
 	rb_set_safe_level_force(safe);
 	FilePathValue(fname);
@@ -974,8 +980,36 @@ rb_require_safe(VALUE fname, int safe)
 					   rb_sourceline());
 	}
 
-	path = rb_str_encode_ospath(fname);
-	found = search_required(path, &path, safe);
+	ipath = rb_str_encode_ospath(fname);
+	if (vm->require_cache.read && RSTRING_PTR(ipath)[0] != '/') {
+	    key = (st_data_t)RSTRING_PTR(ipath);
+	    if (st_lookup(vm->require_cache.tbl, key, &val)) {
+		vals = (char *)val;
+		found = vals[0];
+		if (found) {
+		    /*fprintf(stderr, "FOUND '%s' => '%s'\n", (char *)key, vals);*/
+		    path = rb_str_new_cstr(vals+1);
+                    vals[1] = 0;
+		}
+	    } else {
+		found = search_required(ipath, &path, safe);
+		/*if (found && path)
+		    fprintf(stderr, "MISSING '%s' => '%s'\n", RSTRING_PTR(ipath), RSTRING_PTR(path));*/
+	    }
+	} else {
+	    found = search_required(ipath, &path, safe);
+	    /*if (found && path)
+		fprintf(stderr, "SEARCHING '%s' found '%s'\n", RSTRING_PTR(ipath), RSTRING_PTR(path));*/
+	}
+	if (vm->require_cache.write && RSTRING_PTR(ipath)[0] != '/' && (!found || (found && path))) {
+	    /*fprintf(stderr, "WRITING '%s' => '%s'\n", RSTRING_PTR(ipath), found ? RSTRING_PTR(path) : "");*/
+	    fprintf(vm->require_cache.out, "%s\n", RSTRING_PTR(ipath));
+	    if (found)
+		fprintf(vm->require_cache.out, "%c%s\n", found, RSTRING_PTR(path));
+	    else
+		fprintf(vm->require_cache.out, "%s\n", "");
+	    fsync(fileno(vm->require_cache.out));
+	}
 
 	if (RUBY_DTRACE_FIND_REQUIRE_RETURN_ENABLED()) {
 	    RUBY_DTRACE_FIND_REQUIRE_RETURN(StringValuePtr(fname),
@@ -1154,6 +1188,35 @@ rb_f_autoload_p(VALUE obj, VALUE sym)
     return rb_mod_autoload_p(klass, sym);
 }
 
+void
+require_cache_setup()
+{
+    rb_vm_t *vm = GET_VM();
+    FILE *file;
+    char *env, line1[PATH_MAX+3], line2[PATH_MAX+3];
+
+    if ((env = getenv("REQUIRE_CACHE_WRITE"))) {
+	unsetenv("REQUIRE_CACHE_WRITE", "");
+	vm->require_cache.write = 1;
+	vm->require_cache.out = fopen(env, "w");
+    } else if ((env = getenv("REQUIRE_CACHE_READ"))) {
+	file = fopen(env, "r");
+	if (!file) return;
+
+	vm->require_cache.read = 1;
+	vm->require_cache.tbl = st_init_strtable();
+	while (1) {
+	    if (!fgets(line1, PATH_MAX+2, file)) break;
+	    if (!fgets(line2, PATH_MAX+2, file)) break;
+	    line1[strlen(line1)-1] = 0;
+	    line2[strlen(line2)-1] = 0;
+	    /*fprintf(stderr, "INSERTING '%s' => '%s'\n", line1, line2);*/
+	    st_insert(vm->require_cache.tbl, (st_data_t)ruby_strdup(line1), (st_data_t)ruby_strdup(line2));
+	}
+	fclose(file);
+    }
+}
+
 void
 Init_load()
 {
@@ -1187,4 +1250,6 @@ Init_load()
 
     ruby_dln_librefs = rb_ary_tmp_new(0);
     rb_gc_register_mark_object(ruby_dln_librefs);
+
+    require_cache_setup();
 }
diff --git a/vm.c b/vm.c
index 212f7b01401f68..cb8456bbf96c5a 100644
--- a/vm.c
+++ b/vm.c
@@ -1823,6 +1823,9 @@ ruby_vm_destruct(rb_vm_t *vm)
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
 	struct rb_objspace *objspace = vm->objspace;
 #endif
+	if (vm->require_cache.write)
+	    fclose(vm->require_cache.out);
+
 	rb_gc_force_recycle(vm->self);
 	vm->main_thread = 0;
 	if (th) {
diff --git a/vm_core.h b/vm_core.h
index 73127e65eab41d..a19bba74e3f627 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -377,6 +377,12 @@ typedef struct rb_vm_struct {
     VALUE loaded_features_snapshot;
     struct st_table *loaded_features_index;
     struct st_table *loading_table;
+    struct {
+	unsigned int read:1;
+	struct st_table *tbl;
+	unsigned int write:1;
+	FILE *out;
+    } require_cache;
 
     /* signal */
     struct {