diff --git a/datetime/mod.ts b/datetime/mod.ts
index db66af177..c5e6bf0c4 100644
--- a/datetime/mod.ts
+++ b/datetime/mod.ts
@@ -1,11 +1,13 @@
+export type DateFormat = "mm-dd-yyyy" | "dd-mm-yyyy" | "yyyy-mm-dd";
+
 /**
  * Parse date from string using format string
  *
  * @param {string} dateStr - date string
- * @param {string} format - format string
+ * @param {DateFormat} format - format string
  * @return {Date} Parsed date
  */
-export function parseDate(dateStr: string, format: string): Date {
+export function parseDate(dateStr: string, format: DateFormat): Date {
   let m, d, y: string;
 
   if (format === "mm-dd-yyyy") {
@@ -17,19 +19,32 @@ export function parseDate(dateStr: string, format: string): Date {
   } else if (format === "yyyy-mm-dd") {
     const datePattern = /^(\d{4})-(\d{2})-(\d{2})$/;
     [, y, m, d] = datePattern.exec(dateStr);
+  } else {
+    throw new Error("Invalid date format!");
   }
 
   return new Date(Number(y), Number(m) - 1, Number(d));
 }
 
+export type DateTimeFormat =
+  | "mm-dd-yyyy hh:mm"
+  | "dd-mm-yyyy hh:mm"
+  | "yyyy-mm-dd hh:mm"
+  | "hh:mm mm-dd-yyyy"
+  | "hh:mm dd-mm-yyyy"
+  | "hh:mm yyyy-mm-dd";
+
 /**
  * Parse date & time from string using format string
  *
  * @param {string} dateStr - date & time string
- * @param {string} format - format string
+ * @param {DateTimeFormat} format - format string
  * @return {Date} Parsed date
  */
-export function parseDateTime(datetimeStr: string, format: string): Date {
+export function parseDateTime(
+  datetimeStr: string,
+  format: DateTimeFormat
+): Date {
   let m, d, y, ho, mi: string;
 
   if (format === "mm-dd-yyyy hh:mm") {
@@ -50,6 +65,8 @@ export function parseDateTime(datetimeStr: string, format: string): Date {
   } else if (format === "hh:mm yyyy-mm-dd") {
     const datePattern = /^(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2})$/;
     [, ho, mi, y, m, d] = datePattern.exec(datetimeStr);
+  } else {
+    throw new Error("Invalid datetime format!");
   }
 
   return new Date(Number(y), Number(m) - 1, Number(d), Number(ho), Number(mi));
diff --git a/datetime/test.ts b/datetime/test.ts
index d5c1622cc..c0e0f89b1 100644
--- a/datetime/test.ts
+++ b/datetime/test.ts
@@ -9,7 +9,7 @@ test(function parseDateTime() {
 });
 test(function parseDate() {
   assertEqual(
-    datetime.parseDateTime("01-03-2019", "mm-dd-yyyy"),
+    datetime.parseDate("01-03-2019", "mm-dd-yyyy"),
     new Date(2019, 1, 3)
   );
 });