diff --git a/ext/date/date_core.c b/ext/date/date_core.c
index 7ed21db..448e969 100644
--- a/ext/date/date_core.c
+++ b/ext/date/date_core.c
@@ -6985,12 +6985,14 @@ jisx0301_date(VALUE jd, VALUE y)
 static VALUE
 d_lite_jisx0301(VALUE self)
 {
-    VALUE s;
+    VALUE s, result;
 
     get_d1(self);
     s = jisx0301_date(m_real_local_jd(dat),
 		      m_real_year(dat));
-    return strftimev(RSTRING_PTR(s), self, set_tmx);
+    result = strftimev(RSTRING_PTR(s), self, set_tmx);
+    RB_GC_GUARD(s);
+    return result;
 }
 
 #ifndef NDEBUG
@@ -8298,7 +8300,7 @@ dt_lite_strftime(int argc, VALUE *argv, VALUE self)
 static VALUE
 iso8601_timediv(VALUE self, VALUE n)
 {
-    VALUE fmt;
+    VALUE fmt, result;
 
     n = to_integer(n);
     fmt = rb_usascii_str_new2("T%H:%M:%S");
@@ -8315,7 +8317,9 @@ iso8601_timediv(VALUE self, VALUE n)
 	rb_str_append(fmt, rb_f_sprintf(3, argv));
     }
     rb_str_append(fmt, rb_usascii_str_new2("%:z"));
-    return strftimev(RSTRING_PTR(fmt), self, set_tmx);
+    result = strftimev(RSTRING_PTR(fmt), self, set_tmx);
+    RB_GC_GUARD(fmt);
+    return result;
 }
 
 /*
@@ -8372,7 +8376,7 @@ dt_lite_rfc3339(int argc, VALUE *argv, VALUE self)
 static VALUE
 dt_lite_jisx0301(int argc, VALUE *argv, VALUE self)
 {
-    VALUE n, s;
+    VALUE n, s, result;
 
     rb_scan_args(argc, argv, "01", &n);
 
@@ -8383,8 +8387,10 @@ dt_lite_jisx0301(int argc, VALUE *argv, VALUE self)
 	get_d1(self);
 	s = jisx0301_date(m_real_local_jd(dat),
 			  m_real_year(dat));
-	return rb_str_append(strftimev(RSTRING_PTR(s), self, set_tmx),
-			     iso8601_timediv(self, n));
+	result = rb_str_append(strftimev(RSTRING_PTR(s), self, set_tmx),
+			       iso8601_timediv(self, n));
+	RB_GC_GUARD(s);
+	return result;
     }
 }