diff --git a/tests/run_tests.py b/tests/run_tests.py
index de253c9670..48fc23d4af 100755
--- a/tests/run_tests.py
+++ b/tests/run_tests.py
@@ -75,7 +75,9 @@ set(CTEST_MEMORYCHECK_COMMAND "{valgrind_cmd}")
 set(CTEST_MEMORYCHECK_COMMAND_OPTIONS "--tool=memcheck --leak-check=yes --show-reachable=yes --num-callers=20 --track-fds=yes")
 #set(CTEST_MEMORYCHECK_SUPPRESSIONS_FILE ${{CTEST_SOURCE_DIRECTORY}}/../tests/valgrind.supp)
 set(MEM_CHECK {mem_check})
+if(MEM_CHECK)
 set(ENV{{MEM_CHECK}} ${{MEM_CHECK}})
+endif()
 
 set(CTEST_COVERAGE_COMMAND "gcov")
 set(COVERAGE {coverage})