diff --git a/cmake/PackageDebian.cmake b/cmake/PackageDebian.cmake
index a4b2bc0d3..1bf1cfa13 100644
--- a/cmake/PackageDebian.cmake
+++ b/cmake/PackageDebian.cmake
@@ -26,10 +26,12 @@ if(ENABLE_SSL)
   set(DEPENDS "${DEPENDS}, libssl-dev")
 endif()
 if(ENABLE_UI)
-  if(QT_VERSION VERSION_LESS "6.0.0")
+  if(Qt5_FOUND)
     set(DEPENDS "${DEPENDS}, libqt5widgets5, libqt5network5, libqt5gui5, libqt5core5a")
-  else()
+  elseif(Qt6_FOUND)
     set(DEPENDS "${DEPENDS}, libqt6widgets6, libqt6network6, libqt6gui6, libqt6core6")
+  else()
+    ecbuild_critical("ENABLE_UI is set but neither Qt5 nor Qt6 was found - cannot determine the Debian package's Qt dependencies")
   endif()
 endif()
 set(CPACK_DEBIAN_PACKAGE_DEPENDS "${DEPENDS}")