diff --git a/src/Specs/Builder/ParameterSpecBuilder.php b/src/Specs/Builder/ParameterSpecBuilder.php
index 1df38c8..b6e2728 100644
--- a/src/Specs/Builder/ParameterSpecBuilder.php
+++ b/src/Specs/Builder/ParameterSpecBuilder.php
@@ -30,10 +30,6 @@ class ParameterSpecBuilder implements ParameterSpecBuilderInterface
 {
     protected $regexp = '/
         ^
-        (?:
-            (?<type>(\w+\b(?:\(.*\))?)(?:\s*\|\s*(?-1))*)
-            \s*
-        )
         (?:
             (?<rest>\.{3})
             \s*
@@ -54,6 +50,14 @@ class ParameterSpecBuilder implements ParameterSpecBuilderInterface
                 |
                 true | false | null
             )
+            \s*
+        )?
+        (?:
+            \s*
+            \:
+            \s*
+            (?<type>(\w+\b(?:\(.*\))?)(?:\s*\|\s*(?-1))*)
+            \s*
         )?
         $
         /xi';
@@ -102,7 +106,7 @@ public function build(string $definition): ParameterSpecInterface
 
     protected function buildVariadicParameterSpec(array $matches): VariadicParameterSpec
     {
-        if (isset($matches['default'])) {
+        if (isset($matches['default']) && '' !== $matches['default']) {
             throw new ParameterSpecBuilderException('Variadic parameter should have no default value');
         }
 
diff --git a/tests/Specs/Builder/FunctionSpecBuilderTest.php b/tests/Specs/Builder/FunctionSpecBuilderTest.php
index b0799ca..719582d 100644
--- a/tests/Specs/Builder/FunctionSpecBuilderTest.php
+++ b/tests/Specs/Builder/FunctionSpecBuilderTest.php
@@ -109,9 +109,9 @@ public function testBuildingSpecWithNoReturnTypeIsTheSameAsWithAnyReturnType()
 
     public function testBuildSpecWithParams()
     {
-        $this->parameterSpecBuilderShouldBuildOn('param one', 'param two = "default"', 'rest ...params');
+        $this->parameterSpecBuilderShouldBuildOn('one: param', 'two = "default": param', '...params: rest');
 
-        $spec = $this->builder->build('(param one, param two = "default", rest ...params)');
+        $spec = $this->builder->build('(one: param, two = "default": param, ...params: rest)');
 
         $this->assertInstanceOf(FunctionSpecInterface::class, $spec);
         $this->assertFalse($spec->needsExecutionContext());
diff --git a/tests/Specs/Builder/ParameterSpecBuilderTest.php b/tests/Specs/Builder/ParameterSpecBuilderTest.php
index 4e0bb0b..9c87e84 100644
--- a/tests/Specs/Builder/ParameterSpecBuilderTest.php
+++ b/tests/Specs/Builder/ParameterSpecBuilderTest.php
@@ -69,7 +69,7 @@ public function testBuildingMandatoryParameter()
     {
         $this->extractorDefinitionShouldBuildOn('type');
 
-        $spec = $this->builder->build('type param');
+        $spec = $this->builder->build('param: type');
 
         $this->assertInstanceOf(MandatoryParameterSpec::class, $spec);
 
@@ -81,7 +81,7 @@ public function testBuildingMandatoryParameterWithComplexType()
     {
         $this->extractorDefinitionShouldBuildOn('instance( Some\Class )');
 
-        $spec = $this->builder->build('instance( Some\Class ) param');
+        $spec = $this->builder->build('param : instance( Some\Class )');
 
         $this->assertInstanceOf(MandatoryParameterSpec::class, $spec);
 
@@ -93,7 +93,7 @@ public function testBuildingMandatoryParameterWithVaryingType()
     {
         $this->extractorDefinitionShouldBuildOn('foo|bar');
 
-        $spec = $this->builder->build('foo|bar param');
+        $spec = $this->builder->build('param: foo|bar');
 
         $this->assertInstanceOf(MandatoryParameterSpec::class, $spec);
 
@@ -111,7 +111,7 @@ public function testBuildingOptionalParameter(string $raw_default, $expected_def
     {
         $this->extractorDefinitionShouldBuildOn('type');
 
-        $spec = $this->builder->build('type param = ' . $raw_default);
+        $spec = $this->builder->build('param = ' . $raw_default . ': type');
 
         $this->assertInstanceOf(OptionalParameterSpec::class, $spec);
 
@@ -124,7 +124,7 @@ public function testBuildingVariadicParameter()
     {
         $this->extractorDefinitionShouldBuildOn('type');
 
-        $spec = $this->builder->build('type ...param');
+        $spec = $this->builder->build('...param: type');
 
         $this->assertInstanceOf(VariadicParameterSpec::class, $spec);
 
@@ -138,7 +138,7 @@ public function testBuildingVariadicParameter()
      */
     public function testBuildingVariadicParameterWithDefaultValueShouldThrowException()
     {
-        $this->builder->build('type ...param = []');
+        $this->builder->build('...param = []: type');
     }
 
     /**
@@ -149,7 +149,7 @@ public function testBuildingWhenExtractorFailsShouldAlsoFail()
     {
         $this->extractorDefinitionShouldThrowOn('fail');
 
-        $this->builder->build('fail param');
+        $this->builder->build('param :fail');
     }