diff --git a/latex2mobi-converter/src/main/java/at/ac/tuwien/ims/latex2mobiformulaconv/converter/Converter.java b/latex2mobi-converter/src/main/java/at/ac/tuwien/ims/latex2mobiformulaconv/converter/Converter.java
index c58d667..e1dbbf8 100644
--- a/latex2mobi-converter/src/main/java/at/ac/tuwien/ims/latex2mobiformulaconv/converter/Converter.java
+++ b/latex2mobi-converter/src/main/java/at/ac/tuwien/ims/latex2mobiformulaconv/converter/Converter.java
@@ -265,6 +265,7 @@ private File saveHtmlFile(Document document) {
                 } catch (FileAlreadyExistsException e) {
                     // do nothing
                 }
+                mainCssIs = classLoader.getResourceAsStream(MAIN_CSS_FILENAME);
                 Files.copy(mainCssIs, markupDir.resolve(MAIN_CSS_FILENAME), StandardCopyOption.REPLACE_EXISTING);
 
                 Files.copy(tempFilepath, markupDir.resolve(tempFilepath.getFileName()), StandardCopyOption.REPLACE_EXISTING);