diff --git a/internal/multipart/reader_test.go b/internal/multipart/reader_test.go
index 03a0d7a..a726dce 100644
--- a/internal/multipart/reader_test.go
+++ b/internal/multipart/reader_test.go
@@ -6,6 +6,8 @@ import (
 )
 
 func TestSimple(t *testing.T) {
+	t.Parallel()
+
 	test := struct {
 		Input    []byte
 		Boundary string
@@ -72,6 +74,7 @@ facebook.com
 }
 
 func TestSimpleWithCRLF(t *testing.T) {
+	t.Parallel()
 
 	type tcase struct {
 		Input    []byte
@@ -156,6 +159,8 @@ facebook.com
 }
 
 func TestNoName(t *testing.T) {
+	t.Parallel()
+
 	tests := []struct {
 		Input    []byte
 		Boundary string
@@ -198,6 +203,8 @@ func TestNoName(t *testing.T) {
 }
 
 func TestNoHeader(t *testing.T) {
+	t.Parallel()
+
 	tests := []struct {
 		Input    []byte
 		Boundary string
@@ -236,6 +243,8 @@ func TestNoHeader(t *testing.T) {
 }
 
 func TestNameConflict(t *testing.T) {
+	t.Parallel()
+
 	test := struct {
 		Input    []byte
 		Boundary string
@@ -266,6 +275,8 @@ facebook.com
 }
 
 func TestGetterNil(t *testing.T) {
+	t.Parallel()
+
 	test := struct {
 		Input    []byte
 		Boundary string
diff --git a/typecheck/builtin/any_test.go b/typecheck/builtin/any_test.go
index ee178ff..7ef19d2 100644
--- a/typecheck/builtin/any_test.go
+++ b/typecheck/builtin/any_test.go
@@ -7,6 +7,8 @@ import (
 )
 
 func TestAny_New(t *testing.T) {
+	t.Parallel()
+
 	inst := interface{}(builtin.NewAny())
 
 	switch cast := inst.(type) {
@@ -18,6 +20,7 @@ func TestAny_New(t *testing.T) {
 }
 
 func TestAny_AvailableTypes(t *testing.T) {
+	t.Parallel()
 
 	inst := builtin.NewAny()
 
@@ -52,6 +55,8 @@ func TestAny_AvailableTypes(t *testing.T) {
 }
 
 func TestAny_AlwaysTrue(t *testing.T) {
+	t.Parallel()
+
 	const typeName = "any"
 
 	checker := builtin.NewAny().Checker(typeName)
diff --git a/typecheck/builtin/int_test.go b/typecheck/builtin/int_test.go
index a99b2f0..be43293 100644
--- a/typecheck/builtin/int_test.go
+++ b/typecheck/builtin/int_test.go
@@ -8,6 +8,8 @@ import (
 )
 
 func TestInt_New(t *testing.T) {
+	t.Parallel()
+
 	inst := interface{}(builtin.NewInt())
 
 	switch cast := inst.(type) {
@@ -19,6 +21,7 @@ func TestInt_New(t *testing.T) {
 }
 
 func TestInt_AvailableTypes(t *testing.T) {
+	t.Parallel()
 
 	inst := builtin.NewInt()
 
@@ -52,6 +55,8 @@ func TestInt_AvailableTypes(t *testing.T) {
 }
 
 func TestInt_Values(t *testing.T) {
+	t.Parallel()
+
 	const typeName = "int"
 
 	checker := builtin.NewInt().Checker(typeName)
diff --git a/typecheck/builtin/string_test.go b/typecheck/builtin/string_test.go
index 7794d1b..0c20579 100644
--- a/typecheck/builtin/string_test.go
+++ b/typecheck/builtin/string_test.go
@@ -7,6 +7,8 @@ import (
 )
 
 func TestString_New(t *testing.T) {
+	t.Parallel()
+
 	inst := interface{}(builtin.NewString())
 
 	switch cast := inst.(type) {
@@ -18,6 +20,7 @@ func TestString_New(t *testing.T) {
 }
 
 func TestString_AvailableTypes(t *testing.T) {
+	t.Parallel()
 
 	inst := builtin.NewString()
 
@@ -66,6 +69,8 @@ func TestString_AvailableTypes(t *testing.T) {
 }
 
 func TestString_AnyLength(t *testing.T) {
+	t.Parallel()
+
 	const typeName = "string"
 
 	checker := builtin.NewString().Checker(typeName)
@@ -102,6 +107,7 @@ func TestString_AnyLength(t *testing.T) {
 
 }
 func TestString_FixedLength(t *testing.T) {
+	t.Parallel()
 
 	tests := []struct {
 		Type  string
@@ -145,6 +151,7 @@ func TestString_FixedLength(t *testing.T) {
 
 }
 func TestString_VariableLength(t *testing.T) {
+	t.Parallel()
 
 	tests := []struct {
 		Type  string