diff --git a/day-4/src/main.rs b/day-4/src/main.rs
index 3833cc0..1e5dfd9 100644
--- a/day-4/src/main.rs
+++ b/day-4/src/main.rs
@@ -17,12 +17,16 @@ fn parse_passports(input: &str) -> Result<Vec<HashMap<&str, &str>>, &str> {
                 .trim()
                 .split(|c| c == ' ' || c == '\n')
                 .map(|field| {
-                    let item = field.split_at(3);
+                    let split = field
+                        .find(':')
+                        .ok_or("Invalid passport entry; no separator")?;
+                    let item = field.split_at(split);
+
                     let key = item.0;
                     let value = item
                         .1
                         .strip_prefix(":")
-                        .ok_or("Invalid entry; value too short")?;
+                        .expect("We've already checked the separator exists");
 
                     Ok((key, value))
                 })
@@ -33,13 +37,55 @@ fn parse_passports(input: &str) -> Result<Vec<HashMap<&str, &str>>, &str> {
 
 fn validate_passports(passports: &Vec<HashMap<&str, &str>>) -> usize {
     let required_fields = ["byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"];
+    let rules = [
+        |year: &str| match year.parse() {
+            Ok(1920..=2002) => true,
+            _ => false,
+        },
+        |year: &str| match year.parse() {
+            Ok(2010..=2020) => true,
+            _ => false,
+        },
+        |year: &str| match year.parse() {
+            Ok(2020..=2030) => true,
+            _ => false,
+        },
+        |height: &str| match height.split_at(height.chars().count() - 2) {
+            (height, "cm") => match height.parse() {
+                Ok(150..=193) => true,
+                _ => false,
+            },
+            (height, "in") => match height.parse() {
+                Ok(59..=76) => true,
+                _ => false,
+            },
+            _ => false,
+        },
+        |color: &str| match color.split_at(1) {
+            ("#", code) => code.chars().all(|a| char::is_ascii_hexdigit(&a)),
+            _ => false,
+        },
+        |color: &str| {
+            ["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]
+                .iter()
+                .any(|c| c == &color)
+        },
+        |pid: &str| pid.chars().count() == 9 && pid.chars().all(char::is_numeric),
+    ];
 
     passports
         .iter()
         .filter(|passport| {
             required_fields
                 .iter()
-                .all(|field| passport.contains_key(field))
+                .zip(rules.iter())
+                .all(|(field, rule)| {
+                    if let Some(value) = passport.get(field) {
+                        rule(value)
+                    } else {
+                        false
+                    }
+                })
         })
         .count()
 }