diff --git a/libkmipclient/json.c b/libkmipclient/json.c
index ed8e27c7..570c64f1 100644
--- a/libkmipclient/json.c
+++ b/libkmipclient/json.c
@@ -621,6 +621,10 @@ int kmip_encode_json(const struct kmip_node *node, json_object **obj,
 
 	case KMIP_TYPE_DATE_TIME:
 		tm = gmtime((time_t *)&node->date_time_value);
+		if (tm == NULL) {
+			rc = -EINVAL;
+			goto out;
+		}
 		strftime(outstr, sizeof(outstr), KMIP_ISO8601_TIMESTAMP_UTC,
 			 tm);
 		memb_obj = json_object_new_string(outstr);
diff --git a/libkmipclient/xml.c b/libkmipclient/xml.c
index 22766085..61a4e625 100644
--- a/libkmipclient/xml.c
+++ b/libkmipclient/xml.c
@@ -460,6 +460,10 @@ int kmip_encode_xml(const struct kmip_node *node, xmlNode **xml, bool debug)
 
 	case KMIP_TYPE_DATE_TIME:
 		tm = gmtime((time_t *)&node->date_time_value);
+		if (tm == NULL) {
+			rc = -EINVAL;
+			goto out;
+		}
 		strftime(tmp_str, sizeof(tmp_str), KMIP_ISO8601_TIMESTAMP_UTC,
 			 tm);
 		attr = xmlSetProp(ret_xml, (xmlChar *)KMIP_XML_VALUE,