diff --git a/thunderbird.spec b/thunderbird.spec
index cbb5e55..e31762a 100644
--- a/thunderbird.spec
+++ b/thunderbird.spec
@@ -125,6 +125,14 @@ end}
 
 %global official_branding       1
 %global build_langpacks         1
+
+# Workaround the dreaded "upstream source file changed content" rpmdiff failure that only secalert can waive.
+# If set to .b2 or .b3 ... the processed source file needs to be renamed before upload, e.g.
+# thunderbird-91.9.0.b2.processed-source.tar.xz
+# With does_not_exist it's empty and source file name as is.
+#global buildnum %{?does_not_exist}
+%global buildnum %{?does_not_exist}
+
 Summary:        Mozilla Thunderbird mail/newsgroup client
 Name:           thunderbird
 Version:        91.10.0
@@ -148,7 +156,7 @@ ExcludeArch:    s390 ppc
 # The official tarball has to be always processed by the process-official-tarball
 # script.
 # Link to official tarball: https://archive.mozilla.org/pub/thunderbird/releases/%%{version}%%{?pre_version}/source/thunderbird-%%{version}%%{?pre_version}.source.tar.xz
-Source0:        thunderbird-%{version}%{?pre_version}.processed-source.tar.xz
+Source0:        thunderbird-%{version}%{?pre_version}%{?buildnum}.processed-source.tar.xz
 %if %{build_langpacks}
 Source1:        thunderbird-langpacks-%{version}%{?ext_version}-20220530.tar.xz
 %endif