diff --git a/cmake/thisdd4hep.sh b/cmake/thisdd4hep.sh
index 35d09971f5d9c1bfc3809cbacf2d5373a30f3995..2ceadc4d57ff92370612b453f0e52da5cd02fbc4 100644
--- a/cmake/thisdd4hep.sh
+++ b/cmake/thisdd4hep.sh
@@ -35,7 +35,7 @@ dd4hep_add_path()   {
     path_prefix=${2}
     eval path_value=\$$path_name
     # Prevent duplicates
-    path_value=`echo ${path_value} | tr : '\n' | grep -v ${path_prefix} | tr '\n' : | sed 's|:$||'`
+    path_value=`echo ${path_value} | tr : '\n' | grep -v "${path_prefix}" | tr '\n' : | sed 's|:$||'`
     path_value="${path_prefix}${path_value:+:${path_value}}"
     eval export ${path_name}='${path_value}'
     unset path_name path_prefix path_value
diff --git a/cmake/thisdd4hep_only.sh b/cmake/thisdd4hep_only.sh
index 3f6314a6c9e02e56bd08f76ec01905dd11c4a4f4..81fae3094b8b493477232512cf723e6ec0893480 100644
--- a/cmake/thisdd4hep_only.sh
+++ b/cmake/thisdd4hep_only.sh
@@ -37,7 +37,7 @@ dd4hep_add_path()   {
     path_prefix=${2}
     eval path_value=\$$path_name
     # Prevent duplicates
-    path_value=`echo ${path_value} | tr : '\n' | grep -v ${path_prefix} | tr '\n' : | sed 's|:$||'`
+    path_value=`echo ${path_value} | tr : '\n' | grep -v "${path_prefix}" | tr '\n' : | sed 's|:$||'`
     path_value="${path_prefix}${path_value:+:${path_value}}"
     eval export ${path_name}='${path_value}'
     unset path_name path_prefix path_value