diff --git a/src/core/model/int64x64-cairo.h b/src/core/model/int64x64-cairo.h
index 3357b76dc..07d8d8f84 100644
--- a/src/core/model/int64x64-cairo.h
+++ b/src/core/model/int64x64-cairo.h
@@ -201,7 +201,7 @@ public:
   /** Explicit bool conversion. */
   inline explicit operator bool () const
   {
-    return (_v != 0);
+    return (_v.hi != 0 || _v.lo != 0);
   }
 
   /**