diff --git a/tmc-langs-framework/src/main/java/fi/helsinki/cs/tmc/langs/io/zip/StudentFileAwareZipper.java b/tmc-langs-framework/src/main/java/fi/helsinki/cs/tmc/langs/io/zip/StudentFileAwareZipper.java
index 916ae756b..94c685f40 100644
--- a/tmc-langs-framework/src/main/java/fi/helsinki/cs/tmc/langs/io/zip/StudentFileAwareZipper.java
+++ b/tmc-langs-framework/src/main/java/fi/helsinki/cs/tmc/langs/io/zip/StudentFileAwareZipper.java
@@ -5,6 +5,7 @@
 import org.apache.commons.compress.archivers.zip.ZipArchiveEntry;
 import org.apache.commons.compress.archivers.zip.ZipArchiveOutputStream;
 import org.apache.commons.io.FileUtils;
+import org.apache.commons.io.FilenameUtils;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -109,13 +110,8 @@ private void writeToZip(Path currentPath, ZipArchiveOutputStream zipStream, Path
 
         log.trace("Writing {} to zip", currentPath);
 
-        String name = projectPath.getParent().relativize(currentPath).toString();
-
-        if (Files.isDirectory(currentPath)) {
-            log.trace("{} is a directory", currentPath);
-            // Must be "/", can not be replaces with File.separator
-            name += "/";
-        }
+        Path relativePath = projectPath.getParent().relativize(currentPath);
+        String name = relativePathToZipCompliantName(relativePath, Files.isDirectory(currentPath));
 
         ZipArchiveEntry entry = new ZipArchiveEntry(name);
         zipStream.putArchiveEntry(entry);
@@ -129,4 +125,31 @@ private void writeToZip(Path currentPath, ZipArchiveOutputStream zipStream, Path
         log.trace("Closing entry");
         zipStream.closeArchiveEntry();
     }
+
+    private static String relativePathToZipCompliantName(Path path, boolean isDirectory) {
+        log.trace("Generating zip-compliant filename from Path \"{}\", isDirectory: {}", path, isDirectory);
+        // zip standard says "/" is to be used as the path separator.
+        final char separator = '/';
+
+        StringBuilder sb = new StringBuilder();
+        for (Path part : path) {
+            sb.append(part);
+            sb.append(separator);
+        }
+
+        if (sb.length() == 0) {
+            log.trace("Path didn't have any name elements");
+            return path.toString();
+        }
+
+        if (!isDirectory) {
+            // ZipArchiveEntry assumes the entry represents a directory if and only
+            // if the name ends with a forward slash "/". Remove the last "/" because
+            // this wasn't a directory.
+            log.trace("Path wasn't a directory, removing trailing slash");
+            sb.deleteCharAt(sb.length() - 1);
+        }
+
+        return sb.toString();
+    }
 }