diff --git a/scripts/build.py b/scripts/build.py
index 51bbbf8..1db10a8 100644
--- a/scripts/build.py
+++ b/scripts/build.py
@@ -36,15 +36,23 @@ def get_git_revision(path):
 
 def input_files(repo):
     d = repo / 'data'
-    if not d.exists():
-        return
 
-    # Nur tatsächliche CVE-Datensätze einlesen
+    if not d.is_dir():
+        raise RuntimeError(
+            f'Data directory missing: {d}'
+        )
+
     if repo.name == 'vuln-cve':
-        yield from sorted(d.rglob('CVE-*.json'))
+        files = sorted(d.rglob('CVE-*.json'))
+
+        if not files:
+            raise RuntimeError(
+                f'No CVE records found in {d}'
+            )
+
+        yield from files
         return
 
-    # Andere Quellen unverändert verarbeiten
     yield from sorted(d.rglob('*.json'))