diff --git a/Libraries/LibWeb/HTML/Dates.cpp b/Libraries/LibWeb/HTML/Dates.cpp
index e898898d9a5..684088a4591 100644
--- a/Libraries/LibWeb/HTML/Dates.cpp
+++ b/Libraries/LibWeb/HTML/Dates.cpp
@@ -209,25 +209,6 @@ bool is_valid_time_string(StringView value)
     return true;
 }
 
-// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-time-string
-WebIDL::ExceptionOr<GC::Ref<JS::Date>> parse_time_string(JS::Realm& realm, StringView value)
-{
-    // FIXME: Implement spec compliant time string parsing
-    auto parts = value.split_view(':', SplitBehavior::KeepEmpty);
-    if (parts.size() >= 2) {
-        if (auto hours = parts.at(0).to_number<u32>(); hours.has_value()) {
-            if (auto minutes = parts.at(1).to_number<u32>(); minutes.has_value()) {
-                if (parts.size() >= 3) {
-                    if (auto seconds = parts.at(2).to_number<u32>(); seconds.has_value())
-                        return JS::Date::create(realm, JS::make_time(*hours, *minutes, *seconds, 0));
-                }
-                return JS::Date::create(realm, JS::make_date(0, JS::make_time(*hours, *minutes, 0, 0)));
-            }
-        }
-    }
-    return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Can't parse time string"sv };
-}
-
 // https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-month-component
 static Optional<YearAndMonth> parse_a_month_component(GenericLexer& input)
 {
@@ -440,7 +421,7 @@ static Optional<HourMinuteSecond> parse_a_time_component(GenericLexer& input)
         return {};
 
     // 6. Let second be 0.
-    i32 second = 0;
+    f32 second = 0;
 
     // 7. If position is not beyond the end of input and the character at position is U+003A (:), then:
     if (input.consume_specific(':')) {
@@ -463,18 +444,13 @@ static Optional<HourMinuteSecond> parse_a_time_component(GenericLexer& input)
             return {};
         // Otherwise, interpret the resulting sequence as a base-ten number (possibly with a fractional part). Set second
         // to that number.
-        // NB: The spec doesn't state requirements for what we must do with the fractional part of the second(s) string.
-        //     The spec neither requires that we separately preserve it nor requires that we completely discard it. If we
-        //     did have any reason at all to preserve it, we could parse the string into a float here. But there doesn't
-        //     seem to be any point in doing that, because there’s nothing in the corresponding calling algorithm(s) in the
-        //     spec that takes a milliseconds field and does anything with it anyway.
-        auto maybe_second = second_string.to_number<i32>();
+        auto maybe_second = second_string.to_number<f32>();
         if (!maybe_second.has_value())
             return {};
         second = maybe_second.value();
 
         // 4. If second is not a number in the range 0 ≤ second < 60, then fail.
-        if (second < 0 || second > 60)
+        if (second < 0 || second >= 60)
             return {};
     }
 
@@ -482,6 +458,27 @@ static Optional<HourMinuteSecond> parse_a_time_component(GenericLexer& input)
     return HourMinuteSecond { hour, minute, second };
 }
 
+// https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-time-string
+WebIDL::ExceptionOr<GC::Ref<JS::Date>> parse_time_string(JS::Realm& realm, StringView value)
+{
+    // 1. Let input be the string being parsed.
+    // 2. Let position be a pointer into input, initially pointing at the start of the string.
+    GenericLexer input { value };
+
+    // 3. Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
+    auto hour_minute_second = parse_a_time_component(input);
+    if (!hour_minute_second.has_value())
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Can't parse time string"sv };
+
+    // 4. If position is not beyond the end of input, then fail.
+    if (!input.is_eof())
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Can't parse time string"sv };
+
+    // 5. Let time be the time with hour hour, minute minute, and second second.
+    // 6. Return time.
+    return JS::Date::create(realm, JS::make_time(hour_minute_second->hour, hour_minute_second->minute, hour_minute_second->second, static_cast<i32>(hour_minute_second->second * 1000) % 1000));
+}
+
 // https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-local-date-and-time-string
 Optional<DateAndTime> parse_a_local_date_and_time_string(StringView input_view)
 {
diff --git a/Libraries/LibWeb/HTML/Dates.h b/Libraries/LibWeb/HTML/Dates.h
index a3186299452..05bbcebfca9 100644
--- a/Libraries/LibWeb/HTML/Dates.h
+++ b/Libraries/LibWeb/HTML/Dates.h
@@ -43,7 +43,7 @@ struct YearMonthDay {
 struct HourMinuteSecond {
     i32 hour;
     i32 minute;
-    i32 second;
+    f32 second;
 };
 
 struct DateAndTime {
diff --git a/Libraries/LibWeb/HTML/HTMLInputElement.cpp b/Libraries/LibWeb/HTML/HTMLInputElement.cpp
index 199a0ea76db..6cb987e4270 100644
--- a/Libraries/LibWeb/HTML/HTMLInputElement.cpp
+++ b/Libraries/LibWeb/HTML/HTMLInputElement.cpp
@@ -2209,7 +2209,7 @@ static Optional<double> convert_local_date_and_time_string_to_number(StringView
     auto date = date_and_time.date;
     auto time = date_and_time.time;
 
-    auto date_time = UnixDateTime::from_unix_time_parts(date.year, date.month, date.day, time.hour, time.minute, time.second, 0);
+    auto date_time = UnixDateTime::from_unix_time_parts(date.year, date.month, date.day, time.hour, time.minute, time.second, static_cast<i32>(time.second * 1000) % 1000);
     return date_time.milliseconds_since_epoch();
 }
 
diff --git a/Tests/LibWeb/Text/expected/HTML/HTMLInputElement-invalid-time-digits.txt b/Tests/LibWeb/Text/expected/HTML/HTMLInputElement-invalid-time-digits.txt
index aaecaf93c4a..bf93285b1bb 100644
--- a/Tests/LibWeb/Text/expected/HTML/HTMLInputElement-invalid-time-digits.txt
+++ b/Tests/LibWeb/Text/expected/HTML/HTMLInputElement-invalid-time-digits.txt
@@ -1 +1,6 @@
+Parsed invalid as NaN
+Parsed xx:34:56 as NaN
+Parsed 12:xx:56 as NaN
+Parsed 12:34:xx as NaN
+Parsed 12:34:60 as NaN
 PASS (didn't crash)
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeOverflow.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeOverflow.txt
index 897e3e2ad25..04ffd2307f9 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeOverflow.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeOverflow.txt
@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 49 tests
 
-43 Pass
-6 Fail
+49 Pass
 Pass	[INPUT in DATETIME-LOCAL status] The max attribute is not set
 Pass	[INPUT in DATETIME-LOCAL status] Value is empty string
 Pass	[INPUT in DATETIME-LOCAL status] The max attribute is an invalid local date time string
@@ -11,9 +10,9 @@ Pass	[INPUT in DATETIME-LOCAL status] The max attribute is greater than the valu
 Pass	[INPUT in DATETIME-LOCAL status] The value is an invalid local date time string(hour is greater than 23)
 Pass	[INPUT in DATETIME-LOCAL status] The value if an invalid local date time string(year is two digits)
 Pass	[INPUT in DATETIME-LOCAL status] The value is greater than max
-Fail	[INPUT in DATETIME-LOCAL status] The value is greater than max(with millisecond in 1 digit)
-Fail	[INPUT in DATETIME-LOCAL status] The value is greater than max(with millisecond in 2 digits)
-Fail	[INPUT in DATETIME-LOCAL status] The value is greater than max(with millisecond in 3 digits)
+Pass	[INPUT in DATETIME-LOCAL status] The value is greater than max(with millisecond in 1 digit)
+Pass	[INPUT in DATETIME-LOCAL status] The value is greater than max(with millisecond in 2 digits)
+Pass	[INPUT in DATETIME-LOCAL status] The value is greater than max(with millisecond in 3 digits)
 Pass	[INPUT in DATETIME-LOCAL status] The value is greater than max(Year is 10000 should be valid)
 Pass	[INPUT in DATE status] The max attribute is not set
 Pass	[INPUT in DATE status] Value is empty string
@@ -35,9 +34,9 @@ Pass	[INPUT in TIME status] The value attribute is an invalid time string(second
 Pass	[INPUT in TIME status] The max attribute is greater than value attribute
 Pass	[INPUT in TIME status] The time missing second and minute parts is invalid
 Pass	[INPUT in TIME status] The value attribute is greater than max attribute
-Fail	[INPUT in TIME status] The value is greater than max(with millisecond in 1 digit)
-Fail	[INPUT in TIME status] The value is greater than max(with millisecond in 2 digit)
-Fail	[INPUT in TIME status] The value is greater than max(with millisecond in 3 digit)
+Pass	[INPUT in TIME status] The value is greater than max(with millisecond in 1 digit)
+Pass	[INPUT in TIME status] The value is greater than max(with millisecond in 2 digit)
+Pass	[INPUT in TIME status] The value is greater than max(with millisecond in 3 digit)
 Pass	[INPUT in TIME status] The time missing second part is valid
 Pass	[INPUT in TIME status] The time is max for reversed range
 Pass	[INPUT in TIME status] The time is outside the accepted range for reversed range
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeUnderflow.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeUnderflow.txt
index b75209dfccf..d21e6aa3569 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeUnderflow.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-validity-rangeUnderflow.txt
@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 47 tests
 
-41 Pass
-6 Fail
+47 Pass
 Pass	[INPUT in DATETIME-LOCAL status] The min attribute is not set
 Pass	[INPUT in DATETIME-LOCAL status] Value is empty string
 Pass	[INPUT in DATETIME-LOCAL status] The min attribute is an invalid local date time string
@@ -11,9 +10,9 @@ Pass	[INPUT in DATETIME-LOCAL status] The min attribute is less than the value a
 Pass	[INPUT in DATETIME-LOCAL status] The value is an invalid local date time string(hour is greater than 23)
 Pass	[INPUT in DATETIME-LOCAL status] The value is an invalid local date time string(year is two digits)
 Pass	[INPUT in DATETIME-LOCAL status] The value is less than min
-Fail	[INPUT in DATETIME-LOCAL status] The value is less than min(with millisecond in 1 digit)
-Fail	[INPUT in DATETIME-LOCAL status] The value is less than min(with millisecond in 2 digits)
-Fail	[INPUT in DATETIME-LOCAL status] The value is less than min(with millisecond in 3 digits)
+Pass	[INPUT in DATETIME-LOCAL status] The value is less than min(with millisecond in 1 digit)
+Pass	[INPUT in DATETIME-LOCAL status] The value is less than min(with millisecond in 2 digits)
+Pass	[INPUT in DATETIME-LOCAL status] The value is less than min(with millisecond in 3 digits)
 Pass	[INPUT in DATETIME-LOCAL status] The value is less than min(Year is 10000 should be valid)
 Pass	[INPUT in DATETIME-LOCAL status] The value is greater than max
 Pass	[INPUT in DATE status] The min attribute is not set
@@ -33,9 +32,9 @@ Pass	[INPUT in TIME status] The value attribute is an invalid time string
 Pass	[INPUT in TIME status] The min attribute is less than value attribute
 Pass	[INPUT in TIME status] The time missing second and minute parts is invalid
 Pass	[INPUT in TIME status] The value attribute is less than min attribute
-Fail	[INPUT in TIME status] The value is less than min(with millisecond in 1 digit)
-Fail	[INPUT in TIME status] The value is less than min(with millisecond in 2 digit)
-Fail	[INPUT in TIME status] The value is less than min(with millisecond in 3 digit)
+Pass	[INPUT in TIME status] The value is less than min(with millisecond in 1 digit)
+Pass	[INPUT in TIME status] The value is less than min(with millisecond in 2 digit)
+Pass	[INPUT in TIME status] The value is less than min(with millisecond in 3 digit)
 Pass	[INPUT in TIME status] The time missing second part is valid
 Pass	[INPUT in TIME status] The time is max for reversed range
 Pass	[INPUT in TIME status] The time is outside the accepted range for reversed range
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/the-input-element/input-seconds-leading-zeroes.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/the-input-element/input-seconds-leading-zeroes.txt
new file mode 100644
index 00000000000..f13b515438a
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/the-input-element/input-seconds-leading-zeroes.txt
@@ -0,0 +1,17 @@
+Harness status: OK
+
+Found 12 tests
+
+12 Pass
+Pass	Expected valueAsNumber=946729801000 from 2000-01-01T12:30:01
+Pass	Expected digits unchanged in round-trip of 2000-01-01T12:30:01
+Pass	Expected valueAsNumber=946729800500 from 2000-01-01T12:30:00.5
+Pass	Expected digits unchanged in round-trip of 2000-01-01T12:30:00.5
+Pass	Expected valueAsNumber=946729800040 from 2000-01-01T12:30:00.04
+Pass	Expected digits unchanged in round-trip of 2000-01-01T12:30:00.04
+Pass	Expected valueAsNumber=946729800003 from 2000-01-01T12:30:00.003
+Pass	Expected digits unchanged in round-trip of 2000-01-01T12:30:00.003
+Pass	Expected valueAsNumber=45001000 from 12:30:01
+Pass	Expected valueAsNumber=45000500 from 12:30:00.5
+Pass	Expected valueAsNumber=45000040 from 12:30:00.04
+Pass	Expected valueAsNumber=45000003 from 12:30:00.003
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/HTML/HTMLInputElement-invalid-time-digits.html b/Tests/LibWeb/Text/input/HTML/HTMLInputElement-invalid-time-digits.html
index f4e7cf19cc8..4160f0e378e 100644
--- a/Tests/LibWeb/Text/input/HTML/HTMLInputElement-invalid-time-digits.html
+++ b/Tests/LibWeb/Text/input/HTML/HTMLInputElement-invalid-time-digits.html
@@ -4,10 +4,10 @@
     test(() => {
         const inputElement = document.createElement("input");
         inputElement.type = "time";
-        inputElement.value = "invalid";
-        inputElement.value = "xx:34:56";
-        inputElement.value = "12:xx:56";
-        inputElement.value = "12:34:xx";
+        ["invalid", "xx:34:56", "12:xx:56", "12:34:xx", "12:34:60"].forEach(value => {
+            inputElement.value = value;
+            println(`Parsed ${value} as ${inputElement.valueAsNumber}`);
+        });
         println("PASS (didn't crash)");
     });
 </script>
diff --git a/Tests/LibWeb/Text/input/wpt-import/html/semantics/forms/the-input-element/input-seconds-leading-zeroes.html b/Tests/LibWeb/Text/input/wpt-import/html/semantics/forms/the-input-element/input-seconds-leading-zeroes.html
new file mode 100644
index 00000000000..08beb222f78
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/html/semantics/forms/the-input-element/input-seconds-leading-zeroes.html
@@ -0,0 +1,52 @@
+<!DOCTYPE HTML>
+<meta charset="utf-8">
+<html>
+ <head>
+  <title>HTMLInputElement leading zeroes in seconds/millis</title>
+  <script src="../../../../resources/testharness.js"></script>
+  <script src="../../../../resources/testharnessreport.js"></script>
+ </head>
+ <body>
+  <h3>input times and datetimes with leading zeroes in seconds/millis</h3>
+  <!-- This test ensures that seconds and milliseconds are being
+       output with the appropriate field widths when sanitizing
+       datetime-locals and times, e.g. that we don't see "12:30:1".
+       The spec is not specific about how much precision to use
+       in a sanitized time string, but an invalid string would
+       fail at .valueAsNumber -->
+  <hr>
+  <div id="log"></div>
+
+  <input id="inp">
+  <script>
+    var inp=document.getElementById("inp");
+    var cases = [
+      ["datetime-local", "2000-01-01T12:30:01",     946729801000],
+      ["datetime-local", "2000-01-01T12:30:00.5",   946729800500],
+      ["datetime-local", "2000-01-01T12:30:00.04",  946729800040],
+      ["datetime-local", "2000-01-01T12:30:00.003", 946729800003],
+
+      ["time", "12:30:01",     45001000],
+      ["time", "12:30:00.5",   45000500],
+      ["time", "12:30:00.04",  45000040],
+      ["time", "12:30:00.003", 45000003],
+    ];
+
+    for (var i in cases) {
+      var c = cases[i];
+      test(function() {
+        inp.setAttribute("type", c[0]);
+        inp.value = c[1];
+        assert_equals(inp.valueAsNumber, c[2]);
+      },"Expected valueAsNumber=" +c[2] + " from " + c[1]);
+      if (c[0] == "datetime-local") {
+        test(function() {
+          inp.setAttribute("type", c[0]);
+          inp.value = c[1];
+          assert_in_array(inp.value, [c[1], c[1].replace("T", " ")]);
+        },"Expected digits unchanged in round-trip of " + c[1])
+      }
+    }
+  </script>
+ </body>
+</html>