diff --git a/tools/release/Bootstrap/Step/Repack.pm b/tools/release/Bootstrap/Step/Repack.pm
index 3be2cba3c76..9623775536a 100644
--- a/tools/release/Bootstrap/Step/Repack.pm
+++ b/tools/release/Bootstrap/Step/Repack.pm
@@ -78,6 +78,9 @@ sub Verify {
     # l10n metadiff test
 
     my $verifyDirVersion = catfile($verifyDir, $product . '-' . $version);
+    if (-e $verifyDirVersion) {
+        die "ASSERT: Repack::Verify(): $verifyDirVersion already exists?";
+    }
 
     MkdirWithPath(dir => $verifyDirVersion)
       or die("Cannot mkdir $verifyDirVersion: $!");
diff --git a/tools/release/Bootstrap/Step/Updates.pm b/tools/release/Bootstrap/Step/Updates.pm
index 2450615588a..e5bfede7daf 100644
--- a/tools/release/Bootstrap/Step/Updates.pm
+++ b/tools/release/Bootstrap/Step/Updates.pm
@@ -137,6 +137,11 @@ sub Verify {
 
     # Create verification area.
     my $verifyDirVersion = catfile($verifyDir, $product . '-' . $version);
+
+    if (-e $verifyDirVersion) {
+        die "ASSERT: Updates::Verify(): $verifyDirVersion already exists?";
+    }
+
     MkdirWithPath(dir => $verifyDirVersion) 
       or die("Could not mkdir $verifyDirVersion: $!");