diff --git a/builtins/openui5/CMakeLists.txt b/builtins/openui5/CMakeLists.txt
index a9b00e1a1eab4..b628289405ffb 100644
--- a/builtins/openui5/CMakeLists.txt
+++ b/builtins/openui5/CMakeLists.txt
@@ -1,13 +1,28 @@
 set(OPENUI5_VERSION "1.152.0")
 
-ExternalProject_Add(
-    OPENUI5
-    URL ${lcgpackages}/openui5-runtime-${OPENUI5_VERSION}.zip
-    URL_HASH SHA256=4882023d4760ed4c20602e36dd183b02a538fc7e8bbfda607b6e25bd1cbbcdb1
-    CONFIGURE_COMMAND ""
-    BUILD_COMMAND ""
-    INSTALL_COMMAND ""
-    SOURCE_DIR ${CMAKE_BINARY_DIR}/ui5/distribution
-    TIMEOUT 600
-)
-install(DIRECTORY ${CMAKE_BINARY_DIR}/ui5/distribution/ DESTINATION ${CMAKE_INSTALL_OPENUI5DIR}/distribution/ COMPONENT libraries FILES_MATCHING PATTERN "*")
+if(DEFINED OPENUI5_SOURCE_DIR)
+  # Use an already unpacked openui5 runtime distribution instead of
+  # downloading it, analogous to CLAD_SOURCE_DIR for clad. This allows to
+  # build ROOT without network access.
+  if(NOT EXISTS "${OPENUI5_SOURCE_DIR}/resources/sap-ui-core.js")
+    message(FATAL_ERROR "OPENUI5_SOURCE_DIR=${OPENUI5_SOURCE_DIR} does not contain an openui5 runtime distribution (resources/sap-ui-core.js not found)")
+  endif()
+  file(MAKE_DIRECTORY ${CMAKE_BINARY_DIR}/ui5)
+  execute_process(COMMAND ${CMAKE_COMMAND} -E create_symlink
+     ${OPENUI5_SOURCE_DIR} ${CMAKE_BINARY_DIR}/ui5/distribution)
+  set(_openui5_distribution_dir ${OPENUI5_SOURCE_DIR})
+else()
+  ExternalProject_Add(
+      OPENUI5
+      URL ${lcgpackages}/openui5-runtime-${OPENUI5_VERSION}.zip
+      URL_HASH SHA256=4882023d4760ed4c20602e36dd183b02a538fc7e8bbfda607b6e25bd1cbbcdb1
+      CONFIGURE_COMMAND ""
+      BUILD_COMMAND ""
+      INSTALL_COMMAND ""
+      SOURCE_DIR ${CMAKE_BINARY_DIR}/ui5/distribution
+      TIMEOUT 600
+  )
+  set(_openui5_distribution_dir ${CMAKE_BINARY_DIR}/ui5/distribution)
+endif()
+
+install(DIRECTORY ${_openui5_distribution_dir}/ DESTINATION ${CMAKE_INSTALL_OPENUI5DIR}/distribution/ COMPONENT libraries FILES_MATCHING PATTERN "*")
diff --git a/cmake/modules/SearchInstalledSoftware.cmake b/cmake/modules/SearchInstalledSoftware.cmake
index 74dc7fe9ff9d6..d09e1b8b2eab2 100644
--- a/cmake/modules/SearchInstalledSoftware.cmake
+++ b/cmake/modules/SearchInstalledSoftware.cmake
@@ -1128,10 +1128,12 @@ if(webgui)
         $ENV{OPENUI5DIR} ${CMAKE_BINARY_DIR}/ui5/distribution)
   else()
     if(builtin_openui5)
-      ROOT_CHECK_CONNECTION("builtin_openui5=OFF")
-      if (NO_CONNECTION)
-         message(SEND_ERROR "builtin_openui5=ON requires internet connection, check it or disable feature")
-         list(APPEND HOTFIX_BUILD_FLAGS -Dbuiltin_openui5=OFF)
+      if(NOT DEFINED OPENUI5_SOURCE_DIR)
+        ROOT_CHECK_CONNECTION("builtin_openui5=OFF")
+        if (NO_CONNECTION)
+           message(SEND_ERROR "builtin_openui5=ON requires internet connection, check it or disable feature")
+           list(APPEND HOTFIX_BUILD_FLAGS -Dbuiltin_openui5=OFF)
+        endif()
       endif()
       add_subdirectory(builtins/openui5)
     else()