diff --git a/fdroidserver/common.py b/fdroidserver/common.py
index e02d63c1..497b533f 100644
--- a/fdroidserver/common.py
+++ b/fdroidserver/common.py
@@ -3889,6 +3889,9 @@ def get_certificate(signature_block_file):
                              asn1Spec=rfc2315.SignedData())[0]
     try:
         certificates = content.getComponentByName('certificates')
+        if len(certificates) != 1:
+            logging.error("Multiple certificates found.")
+            return None
         cert = certificates[0].getComponentByName('certificate')
     except PyAsn1Error:
         logging.error("Certificates not found.")