diff --git a/arrow-cast/src/parse.rs b/arrow-cast/src/parse.rs
index 710a6a4979c1..4acd2b3376be 100644
--- a/arrow-cast/src/parse.rs
+++ b/arrow-cast/src/parse.rs
@@ -206,7 +206,7 @@ pub fn string_to_datetime<T: TimeZone>(
 
     if tz_offset == 32 {
         // Decimal overrun
-        while bytes[tz_offset].is_ascii_digit() && tz_offset < bytes.len() {
+        while tz_offset < bytes.len() && bytes[tz_offset].is_ascii_digit() {
             tz_offset += 1;
         }
     }
@@ -1083,6 +1083,22 @@ mod tests {
         }
     }
 
+    #[test]
+    fn string_to_timestamp_naive() {
+        let cases = [
+            "2018-11-13T17:11:10.011375885995",
+            "2030-12-04T17:11:10.123",
+            "2030-12-04T17:11:10.1234",
+            "2030-12-04T17:11:10.123456",
+        ];
+        for case in cases {
+            let chrono =
+                NaiveDateTime::parse_from_str(case, "%Y-%m-%dT%H:%M:%S%.f").unwrap();
+            let custom = string_to_datetime(&Utc, case).unwrap();
+            assert_eq!(chrono, custom.naive_utc())
+        }
+    }
+
     #[test]
     fn string_to_timestamp_invalid() {
         // Test parsing invalid formats