diff --git a/cmake/modules/DuneXtCommonMacros.cmake b/cmake/modules/DuneXtCommonMacros.cmake
index 5b305e1e3a1add58bfe5346a57a6240c83846637..97e75cfba140575fa327232f943fb0f2c03db4dc 100644
--- a/cmake/modules/DuneXtCommonMacros.cmake
+++ b/cmake/modules/DuneXtCommonMacros.cmake
@@ -50,7 +50,9 @@ macro(add_format)
     find_program(FORMAT NAMES clang-format clang-format-3.4 clang-format-3.5 clang-format-3.6 clang-format-3.7 clang-format-3.8 clang-format-3.9)
     if(EXISTS ${FORMAT})
         message(STATUS "adding format target")
-        add_custom_target( format SOURCES ${ARGN} )
+	if (NOT TARGET format)
+            add_custom_target( format SOURCES ${ARGN} )
+        endif (NOT TARGET format)
         foreach(_file ${ARGN})
             string(REPLACE "/" "_" fn ${_file})
             if(NOT EXISTS ${_file})
diff --git a/dune/xt/CMakeLists.txt b/dune/xt/CMakeLists.txt
index 8b0d739130672512cf21b59097708d37cff9851a..5ca7c1b3c20328274fe26caa8336b55ece72b29c 100644
--- a/dune/xt/CMakeLists.txt
+++ b/dune/xt/CMakeLists.txt
@@ -27,7 +27,7 @@ dune_library_add_sources(dunextcommon SOURCES ${lib_dune_xt_common_sources})
 add_analyze(${lib_dune_xt_common_sources})
 FILE( GLOB_RECURSE _header "${CMAKE_CURRENT_SOURCE_DIR}/*.hh" )
 
-add_format(${lib_dune_xt_common_sources} ${test_sources} ${_header})
+add_format(${lib_dune_xt_common_sources} ${_header})
 install(DIRECTORY ${DUNE_XT_COMMON_TEST_DIR}/gtest
         DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/dune/xt/test/
         FILES_MATCHING PATTERN "*")
diff --git a/dune/xt/common/test/CMakeLists.txt b/dune/xt/common/test/CMakeLists.txt
index 7b401accd6b7b0dc682b5c17cde28f4daf80b009..cb181cf6b0b9bd22b4d04d985858981ffe4145e2 100644
--- a/dune/xt/common/test/CMakeLists.txt
+++ b/dune/xt/common/test/CMakeLists.txt
@@ -14,5 +14,7 @@ DEPENDENCYCHECK( ${xtcommon} )
 set_source_files_properties( ${DUNE_HEADERS} PROPERTIES HEADER_FILE_ONLY 1 )
 
 BEGIN_TESTCASES(dunextcommon)
- 
-END_TESTCASES()
\ No newline at end of file
+
+add_format(${test_sources})
+
+END_TESTCASES()