diff --git a/Modules/ExternalProject-gitupdate.cmake.in b/Modules/ExternalProject-gitupdate.cmake.in
index 461e323540..0de2372ecf 100644
--- a/Modules/ExternalProject-gitupdate.cmake.in
+++ b/Modules/ExternalProject-gitupdate.cmake.in
@@ -5,7 +5,7 @@ cmake_minimum_required(VERSION 3.5)
 
 function(get_hash_for_ref ref out_var err_var)
   execute_process(
-    COMMAND "@git_EXECUTABLE@" rev-parse "${ref}^{commit}"
+    COMMAND "@git_EXECUTABLE@" rev-parse "${ref}^0"
     WORKING_DIRECTORY "@work_dir@"
     RESULT_VARIABLE error_code
     OUTPUT_VARIABLE ref_hash