diff --git a/cronexpr_parse.go b/cronexpr_parse.go
index 289ad53..aeb8296 100644
--- a/cronexpr_parse.go
+++ b/cronexpr_parse.go
@@ -54,6 +54,7 @@ var (
 var (
 	numberTokens = map[string]int{
 		"0": 0, "1": 1, "2": 2, "3": 3, "4": 4, "5": 5, "6": 6, "7": 7, "8": 8, "9": 9,
+		"00": 0, "01": 1, "02": 2, "03": 3, "04": 4, "05": 5, "06": 6, "07": 7, "08": 8, "09": 9,
 		"10": 10, "11": 11, "12": 12, "13": 13, "14": 14, "15": 15, "16": 16, "17": 17, "18": 18, "19": 19,
 		"20": 20, "21": 21, "22": 22, "23": 23, "24": 24, "25": 25, "26": 26, "27": 27, "28": 28, "29": 29,
 		"30": 30, "31": 31, "32": 32, "33": 33, "34": 34, "35": 35, "36": 36, "37": 37, "38": 38, "39": 39,
@@ -119,7 +120,7 @@ var (
 		min:          0,
 		max:          59,
 		defaultList:  genericDefaultList[0:60],
-		valuePattern: `[0-9]|[1-5][0-9]`,
+		valuePattern: `0?[0-9]|[1-5][0-9]`,
 		atoi:         atoi,
 	}
 	minuteDescriptor = fieldDescriptor{
@@ -127,7 +128,7 @@ var (
 		min:          0,
 		max:          59,
 		defaultList:  genericDefaultList[0:60],
-		valuePattern: `[0-9]|[1-5][0-9]`,
+		valuePattern: `0?[0-9]|[1-5][0-9]`,
 		atoi:         atoi,
 	}
 	hourDescriptor = fieldDescriptor{
@@ -135,7 +136,7 @@ var (
 		min:          0,
 		max:          23,
 		defaultList:  genericDefaultList[0:24],
-		valuePattern: `[0-9]|1[0-9]|2[0-3]`,
+		valuePattern: `0?[0-9]|1[0-9]|2[0-3]`,
 		atoi:         atoi,
 	}
 	domDescriptor = fieldDescriptor{
@@ -143,7 +144,7 @@ var (
 		min:          1,
 		max:          31,
 		defaultList:  genericDefaultList[1:32],
-		valuePattern: `[1-9]|[12][0-9]|3[01]`,
+		valuePattern: `0?[1-9]|[12][0-9]|3[01]`,
 		atoi:         atoi,
 	}
 	monthDescriptor = fieldDescriptor{
@@ -151,7 +152,7 @@ var (
 		min:          1,
 		max:          12,
 		defaultList:  genericDefaultList[1:13],
-		valuePattern: `[1-9]|1[012]|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec|january|february|march|april|march|april|june|july|august|september|october|november|december`,
+		valuePattern: `0?[1-9]|1[012]|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec|january|february|march|april|march|april|june|july|august|september|october|november|december`,
 		atoi: func(s string) int {
 			return monthTokens[s]
 		},
@@ -161,7 +162,7 @@ var (
 		min:          0,
 		max:          6,
 		defaultList:  genericDefaultList[0:7],
-		valuePattern: `[0-7]|sun|mon|tue|wed|thu|fri|sat|sunday|monday|tuesday|wednesday|thursday|friday|saturday`,
+		valuePattern: `0?[0-7]|sun|mon|tue|wed|thu|fri|sat|sunday|monday|tuesday|wednesday|thursday|friday|saturday`,
 		atoi: func(s string) int {
 			return dowTokens[s]
 		},