diff --git a/internal/preproc/filereader_test.go b/internal/preproc/filereader_test.go
index bd0f472..76c4e60 100644
--- a/internal/preproc/filereader_test.go
+++ b/internal/preproc/filereader_test.go
@@ -8,10 +8,10 @@ import (
 
 func TestDiskFileReader_ReadLines_LibraryIncludes(t *testing.T) {
 	origPath := os.Getenv("C65LIBPATH")
-	defer os.Setenv("C65LIBPATH", origPath)
+	defer func() { _ = os.Setenv("C65LIBPATH", origPath) }()
 
 	libPath, _ := filepath.Abs("filereader_mocks/lib")
-	os.Setenv("C65LIBPATH", libPath)
+	_ = os.Setenv("C65LIBPATH", libPath)
 
 	// Now create reader
 	reader := NewDiskFileReader()
@@ -54,9 +54,9 @@ func TestDiskFileReader_ReadLines_LibraryIncludes(t *testing.T) {
 
 func TestDiskFileReader_ReadLines_LibraryWithoutEnv(t *testing.T) {
 	origPath := os.Getenv("C65LIBPATH")
-	defer os.Setenv("C65LIBPATH", origPath)
+	defer func() { _ = os.Setenv("C65LIBPATH", origPath) }()
 
-	os.Setenv("C65LIBPATH", "")
+	_ = os.Setenv("C65LIBPATH", "")
 
 	// Now create reader
 	reader := NewDiskFileReader()