diff --git a/Code/Mantid/Build/Jenkins/buildscript b/Code/Mantid/Build/Jenkins/buildscript
index 49d3bbefff971abf2293aa50cccde3ad44beacf2..5af020f55235a190f73a01db5c3725184ed8200c 100755
--- a/Code/Mantid/Build/Jenkins/buildscript
+++ b/Code/Mantid/Build/Jenkins/buildscript
@@ -21,7 +21,9 @@ if [[ ${JOB_NAME} == *clang* ]]; then
   clang --version
   export CC=clang
   export CXX=clang++
-  if [[ -e $WORKSPACE/build/CMakeCache.txt ]]; then
+  #check if CMakeCache.txt exists and if so that the cxx compiler is clang++
+  #only needed with incremental builds. Clean builds delete this directory in a later step. 
+  if [[ -e $WORKSPACE/build/CMakeCache.txt ]] && [[ ${JOB_NAME} != *clean* ]]; then
     COMPILERFILEPATH=`grep 'CMAKE_CXX_COMPILER:FILEPATH' $WORKSPACE/build/CMakeCache.txt` 
     if [[ $COMPILERFILEPATH != *clang++* ]]; then 
       # Removing the build directory entirely guarantees clang is used.