diff --git a/src/vmime/net/smtp/SMTPChunkingOutputStreamAdapter.cpp b/src/vmime/net/smtp/SMTPChunkingOutputStreamAdapter.cpp
index 5f59e381..35ff4e0d 100644
--- a/src/vmime/net/smtp/SMTPChunkingOutputStreamAdapter.cpp
+++ b/src/vmime/net/smtp/SMTPChunkingOutputStreamAdapter.cpp
@@ -141,7 +141,8 @@ void SMTPChunkingOutputStreamAdapter::flush()
 	sendChunk(m_buffer, m_bufferSize, /* last */ true);
 	m_bufferSize = 0;
 
-	m_progress->stop(m_totalSize);
+	if (m_progress)
+		m_progress->stop(m_totalSize);
 }