diff --git a/Libraries/LibCore/CFile.cpp b/Libraries/LibCore/CFile.cpp
index 38b5b75a0c..dfa5b2c073 100644
--- a/Libraries/LibCore/CFile.cpp
+++ b/Libraries/LibCore/CFile.cpp
@@ -26,6 +26,7 @@ bool CFile::open(int fd, CIODevice::OpenMode mode, ShouldCloseFileDescription sh
 
 bool CFile::open(CIODevice::OpenMode mode)
 {
+    ASSERT(!m_filename.is_null());
     int flags = 0;
     if ((mode & CIODevice::ReadWrite) == CIODevice::ReadWrite) {
         flags |= O_RDWR | O_CREAT;