diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index 4fe56e763..56440f6df 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -33,6 +33,7 @@
 - @xen-orchestra/backups patch
 - @xen-orchestra/fs major
 - vhd-lib major
+- xo-vmdk-to-vhd patch
 - xo-server minor
 - xo-web patch
 
diff --git a/packages/vhd-lib/Vhd/VhdDirectory.js b/packages/vhd-lib/Vhd/VhdDirectory.js
index f4fe8ae9e..23af9ff1f 100644
--- a/packages/vhd-lib/Vhd/VhdDirectory.js
+++ b/packages/vhd-lib/Vhd/VhdDirectory.js
@@ -251,7 +251,7 @@ exports.VhdDirectory = class VhdDirectory extends VhdAbstract {
   async mergeBlock(child, blockId, isResumingMerge = false) {
     const childBlockPath = child._getFullBlockPath?.(blockId)
     if (
-      childBlockPath !== undefined ||
+      childBlockPath === undefined ||
       this._handler !== child._handler ||
       child.compressionType !== this.compressionType ||
       child.compressionType === 'MIXED'