diff --git a/src/DataValues/DecimalValue.php b/src/DataValues/DecimalValue.php
index 96c9518..beb7e6a 100644
--- a/src/DataValues/DecimalValue.php
+++ b/src/DataValues/DecimalValue.php
@@ -46,7 +46,7 @@ class DecimalValue extends DataValueObject {
 	 * Constructs a new DecimalValue object, representing the given value.
 	 *
 	 * @param string|int|float $value If given as a string, the value must match
-	 *                         QUANTITY_VALUE_PATTERN.
+	 *  QUANTITY_VALUE_PATTERN. The leading plus sign is optional.
 	 *
 	 * @throws IllegalValueException
 	 */
@@ -91,8 +91,8 @@ private function convertToDecimal( $number ) {
 			throw new InvalidArgumentException( '$number must not be NAN or INF.' );
 		}
 
-		if ( is_int( $number ) || ( $number === floor( $number ) ) ) {
-			$decimal = strval( abs( (int)$number ) );
+		if ( is_int( $number ) || $number === (float)(int)$number ) {
+			$decimal = strval( (int)abs( $number ) );
 		} else {
 			$decimal = trim( number_format( abs( $number ), 100, '.', '' ), '0' );
 
@@ -101,7 +101,7 @@ private function convertToDecimal( $number ) {
 			}
 
 			if ( substr( $decimal, -1 ) === '.' ) {
-				$decimal .= '0';
+				$decimal = substr( $decimal, 0, -1 );
 			}
 		}
 
diff --git a/tests/DataValues/DecimalValueTest.php b/tests/DataValues/DecimalValueTest.php
index bf901c7..774d9dc 100644
--- a/tests/DataValues/DecimalValueTest.php
+++ b/tests/DataValues/DecimalValueTest.php
@@ -33,6 +33,7 @@ public function validConstructorArgumentsProvider() {
 		$argLists[] = array( 4.2 );
 		$argLists[] = array( -4.2 );
 		$argLists[] = array( '+4.2' );
+		$argLists[] = array( " +4.2\n" );
 		$argLists[] = array( 0 );
 		$argLists[] = array( 0.2 );
 		$argLists[] = array( '-0.42' );
@@ -41,9 +42,10 @@ public function validConstructorArgumentsProvider() {
 		$argLists[] = array( '+0' );
 		$argLists[] = array( '+0.0' );
 		$argLists[] = array( '+0.000' );
+		$argLists[] = array( '+1.' . str_repeat( '0', 124 ) );
 		$argLists[] = array( '+1.0' . str_repeat( ' ', 124 ) );
 		$argLists[] = array( '4.2' );
-		$argLists[] = array( ' 4.2' );
+		$argLists[] = array( " 4.2\n" );
 
 		return $argLists;
 	}
@@ -57,11 +59,13 @@ public function invalidConstructorArgumentsProvider() {
 		$argLists[] = array( '--4.2' );
 		$argLists[] = array( '-+4.2' );
 		$argLists[] = array( '+-4.2' );
+		$argLists[] = array( '+/-0' );
 		$argLists[] = array( '-.42' );
 		$argLists[] = array( '+.42' );
 		$argLists[] = array( '.42' );
 		$argLists[] = array( '.0' );
 		$argLists[] = array( '-00' );
+		$argLists[] = array( '−1' );
 		$argLists[] = array( '+01.2' );
 		$argLists[] = array( 'x2' );
 		$argLists[] = array( '2x' );
@@ -176,6 +180,12 @@ public function getValueProvider() {
 		$argLists[] = array( new DecimalValue( '-0' ), '+0' );
 		$argLists[] = array( new DecimalValue( '+0.0' ), '+0.0' );
 		$argLists[] = array( new DecimalValue( '+0' ), '+0' );
+		$argLists[] = array( new DecimalValue( 2147483649 ), '+2147483649' );
+		$argLists[] = array( new DecimalValue( 1000000000000000 ), '+1000000000000000' );
+		$argLists[] = array(
+			new DecimalValue( 1 + 1e-14 / 3 ),
+			'+1.0000000000000033306690738754696212708950042724609375'
+		);
 
 		return $argLists;
 	}