diff --git a/pkgs/development/tools/build-managers/cmake/setup-hook.sh b/pkgs/development/tools/build-managers/cmake/setup-hook.sh
index 8fdf64417dd3..802c7343a854 100755
--- a/pkgs/development/tools/build-managers/cmake/setup-hook.sh
+++ b/pkgs/development/tools/build-managers/cmake/setup-hook.sh
@@ -3,10 +3,11 @@ addCMakeParams() {
 }
 
 fixCmakeFiles() {
+    # Replace occurences of /usr and /opt by /var/empty.
     echo "fixing cmake files..."
     find "$1" \( -type f -name "*.cmake" -o -name "*.cmake.in" -o -name CMakeLists.txt \) -print |
         while read fn; do
-            sed -e 's|/usr|/var/empty|g' -e 's|/opt|/var/empty|g' < "$fn" > "$fn.tmp"
+            sed -e 's^/usr\([ /]\|$\)^/var/empty\1^g' -e 's^/opt\([ /]\|$\)^/var/empty\1^g' < "$fn" > "$fn.tmp"
             mv "$fn.tmp" "$fn"
         done
 }