diff --git a/Libraries/LibWeb/HTML/HTMLInputElement.cpp b/Libraries/LibWeb/HTML/HTMLInputElement.cpp
index 046c224d811..43b72e2cb16 100644
--- a/Libraries/LibWeb/HTML/HTMLInputElement.cpp
+++ b/Libraries/LibWeb/HTML/HTMLInputElement.cpp
@@ -3098,10 +3098,20 @@ bool HTMLInputElement::suffering_from_an_overflow() const
 // https://html.spec.whatwg.org/multipage/input.html#the-step-attribute%3Asuffering-from-a-step-mismatch
 bool HTMLInputElement::suffering_from_a_step_mismatch() const
 {
-    // When the element has an allowed value step, and the result of applying the algorithm to convert a string to a number to the string given by the element's
-    // value is a number, and that number subtracted from the step base is not an integral multiple of the allowed value step, the element is suffering from a step mismatch.
-    // FIXME: Implement this.
-    return false;
+    // When the element has an allowed value step,
+    auto maybe_allowed_value_step = allowed_value_step();
+    if (!maybe_allowed_value_step.has_value())
+        return false;
+    double allowed_value_step = *maybe_allowed_value_step;
+    // and the result of applying the algorithm to convert a string to a number to the string given by the element's
+    // value is a number,
+    auto maybe_number = convert_string_to_number(value());
+    if (!maybe_number.has_value())
+        return false;
+    double number = maybe_number.value();
+    // and that number subtracted from the step base is not an integral multiple of the allowed value step, the element
+    // is suffering from a step mismatch.
+    return fmod(step_base() - number, allowed_value_step) != 0;
 }
 
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#suffering-from-bad-input
diff --git a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-checkValidity.txt b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-checkValidity.txt
index ce83c6ac33b..a9d6ab0bf27 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-checkValidity.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/html/semantics/forms/constraints/form-validation-checkValidity.txt
@@ -2,8 +2,8 @@ Harness status: OK
 
 Found 130 tests
 
-90 Pass
-40 Fail
+108 Pass
+22 Fail
 Pass	[INPUT in TEXT status] no constraint
 Pass	[INPUT in TEXT status] no constraint (in a form)
 Pass	[INPUT in TEXT status] not suffering from being too long
@@ -68,32 +68,32 @@ Pass	[INPUT in DATETIME-LOCAL status] suffering from being missing
 Pass	[INPUT in DATETIME-LOCAL status] suffering from being missing (in a form)
 Pass	[INPUT in DATE status] no constraint
 Pass	[INPUT in DATE status] no constraint (in a form)
-Fail	[INPUT in DATE status] suffering from an overflow
-Fail	[INPUT in DATE status] suffering from an overflow (in a form)
-Fail	[INPUT in DATE status] suffering from an underflow
-Fail	[INPUT in DATE status] suffering from an underflow (in a form)
-Fail	[INPUT in DATE status] suffering from a step mismatch
-Fail	[INPUT in DATE status] suffering from a step mismatch (in a form)
+Pass	[INPUT in DATE status] suffering from an overflow
+Pass	[INPUT in DATE status] suffering from an overflow (in a form)
+Pass	[INPUT in DATE status] suffering from an underflow
+Pass	[INPUT in DATE status] suffering from an underflow (in a form)
+Pass	[INPUT in DATE status] suffering from a step mismatch
+Pass	[INPUT in DATE status] suffering from a step mismatch (in a form)
 Pass	[INPUT in DATE status] suffering from being missing
 Pass	[INPUT in DATE status] suffering from being missing (in a form)
 Pass	[INPUT in MONTH status] no constraint
 Pass	[INPUT in MONTH status] no constraint (in a form)
-Fail	[INPUT in MONTH status] suffering from an overflow
-Fail	[INPUT in MONTH status] suffering from an overflow (in a form)
-Fail	[INPUT in MONTH status] suffering from an underflow
-Fail	[INPUT in MONTH status] suffering from an underflow (in a form)
-Fail	[INPUT in MONTH status] suffering from a step mismatch
-Fail	[INPUT in MONTH status] suffering from a step mismatch (in a form)
+Pass	[INPUT in MONTH status] suffering from an overflow
+Pass	[INPUT in MONTH status] suffering from an overflow (in a form)
+Pass	[INPUT in MONTH status] suffering from an underflow
+Pass	[INPUT in MONTH status] suffering from an underflow (in a form)
+Pass	[INPUT in MONTH status] suffering from a step mismatch
+Pass	[INPUT in MONTH status] suffering from a step mismatch (in a form)
 Pass	[INPUT in MONTH status] suffering from being missing
 Pass	[INPUT in MONTH status] suffering from being missing (in a form)
 Pass	[INPUT in WEEK status] no constraint
 Pass	[INPUT in WEEK status] no constraint (in a form)
-Fail	[INPUT in WEEK status] suffering from an overflow
-Fail	[INPUT in WEEK status] suffering from an overflow (in a form)
-Fail	[INPUT in WEEK status] suffering from an underflow
-Fail	[INPUT in WEEK status] suffering from an underflow (in a form)
-Fail	[INPUT in WEEK status] suffering from a step mismatch
-Fail	[INPUT in WEEK status] suffering from a step mismatch (in a form)
+Pass	[INPUT in WEEK status] suffering from an overflow
+Pass	[INPUT in WEEK status] suffering from an overflow (in a form)
+Pass	[INPUT in WEEK status] suffering from an underflow
+Pass	[INPUT in WEEK status] suffering from an underflow (in a form)
+Pass	[INPUT in WEEK status] suffering from a step mismatch
+Pass	[INPUT in WEEK status] suffering from a step mismatch (in a form)
 Pass	[INPUT in WEEK status] suffering from being missing
 Pass	[INPUT in WEEK status] suffering from being missing (in a form)
 Pass	[INPUT in TIME status] no constraint