diff --git a/tools/cmake_call.sh b/tools/cmake_call.sh
index f317783b..006c7b58 100755
--- a/tools/cmake_call.sh
+++ b/tools/cmake_call.sh
@@ -2,7 +2,7 @@
 
 : ${R_HOME=$(R RHOME)}
 RSCRIPT_BIN=${R_HOME}/bin/Rscript
-NCORES=`${RSCRIPT_BIN} -e "cat(min(2, parallel::detectCores(logical = FALSE)))"`
+NCORES=`${RSCRIPT_BIN} -e "cat(min(2, na.omit(parallel::detectCores(logical = FALSE))))"`
 
 cd src