diff --git a/core/lib/Drupal/Component/Utility/Number.php b/core/lib/Drupal/Component/Utility/Number.php
index f8d7f0fbd9..6d7d5ee768 100644
--- a/core/lib/Drupal/Component/Utility/Number.php
+++ b/core/lib/Drupal/Component/Utility/Number.php
@@ -37,9 +37,13 @@ class Number {
   public static function normalize($number) {
     // Convert non-strings to strings, for consistent and lossless processing.
     if (is_float($number)) {
+      // If the float has less significant decimals than the number we can
+      // guarantee, convert it to a stirng directly.
       if (preg_match(sprintf('/^\d+\.\d{1,%d}$/', static::IEEE_754_DOUBLE_GUARANTEED_SIGNIFICANT_DECIMALS), (string) $number)) {
         return (string) $number;
       }
+      // For floats with more significant decimals than the number we can
+      // guarantee, discard the unguaranteed ones.
       return rtrim(number_format($number, self::IEEE_754_DOUBLE_GUARANTEED_SIGNIFICANT_DECIMALS, '.', ''), '0');
     }
     elseif (is_int($number)) {
@@ -92,7 +96,7 @@ public static function countSignificantDecimals($number) {
    * @param int|float|string $step
    *   The step scale factor. Must be positive. If this is a string, it must be
    *   formatted as an integer or a float.
-   * @param float $offset
+   * @param float|null $offset
    *   (optional) An offset, to which the difference must be a multiple of the
    *   given step.
    *
@@ -101,12 +105,15 @@ public static function countSignificantDecimals($number) {
    *
    * @see http://opensource.apple.com/source/WebCore/WebCore-1298/html/NumberInputType.cpp
    */
-  public static function validStep($value, $step, $offset = null) {
+  public static function validStep($value, $step, $offset = NULL) {
     // Confirm the step is positive.
     if ($step <= 0) {
       return FALSE;
     }
 
+    // Convert the value to a float so we can evaluate the precision later.
+    // Because subtracting the offset may change the value's precision, we only
+    // do so if it was set explicitly (is not null).
     $float_value = (float) abs(is_null($offset) ? $value : $value - $offset);
 
     // The expected number significant decimals is dictated by the step.
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/DecimalItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/DecimalItem.php
index 44ad5b4704..1b35b80738 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/DecimalItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/DecimalItem.php
@@ -102,6 +102,10 @@ public function getConstraints() {
         ]
       ],
     ]);
+    $constraints[] = $constraint_manager->create('Range', [
+      'min' => 0,
+      'max' => Number::IEEE_754_DOUBLE_GUARANTEED_SIGNIFICANT_DECIMALS,
+    ]);
 
     return $constraints;
   }
diff --git a/core/tests/Drupal/Tests/Component/Utility/NumberTest.php b/core/tests/Drupal/Tests/Component/Utility/NumberTest.php
index 7cd2f050bc..b5e393629d 100644
--- a/core/tests/Drupal/Tests/Component/Utility/NumberTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/NumberTest.php
@@ -167,7 +167,7 @@ public static function providerTestValidStep() {
       // Precision of the value is higher than that of the step.
       [990088999.0099, 0.001, FALSE],
       [990088999.0099, 0.01, FALSE],
-      
+
       // Ensure floats with more significant decimals that the guaranteed
       // minimum are normalized.
       [0.00000000000000900009, 0.00000000000000100001, TRUE],