diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 2431e40..2f54264 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -50,6 +50,12 @@
             ${CMAKE_CURRENT_SOURCE_DIR}/../include/psa/crypto_values.h
             ${CMAKE_CURRENT_SOURCE_DIR}/../include/psa/crypto_extra.h
     )
+    # CMake generate sub-makefile for each target and call it in subprocess. Without
+    # this command, cmake will generate ruler in each sub makefile. As a result,
+    # they will conflict under parllel build.
+    # With this line, only 4 sub-makefiles include above command, that reduces
+    # conflict risk.
+    add_custom_target(test_suite_generated_data DEPENDS ${generated_data_files})
 else()
     foreach(file ${base_generated_data_files})
         link_to_source(${file})