diff --git a/src/trapping/cfrfme.cpp b/src/trapping/cfrfme.cpp
index f4df0fe3c5e37706f6c34792c4169ed1e6e39675..22c46110e1b51e6f5981e298f269f6b717da8418 100644
--- a/src/trapping/cfrfme.cpp
+++ b/src/trapping/cfrfme.cpp
@@ -278,7 +278,7 @@ void frfme(string data_file, string output_path) {
 	  tfrfme.write(reinterpret_cast<char *>(&nkv), sizeof(int));
 	  tfrfme.write(reinterpret_cast<char *>(&nxv), sizeof(int));
 	  tfrfme.write(reinterpret_cast<char *>(&nyv), sizeof(int));
-	  tfrfme.write(reinterpret_cast<char *>(&nxv), sizeof(int));
+	  tfrfme.write(reinterpret_cast<char *>(&nzv), sizeof(int));
 	  tfrfme.write(reinterpret_cast<char *>(&vk), sizeof(double));
 	  tfrfme.write(reinterpret_cast<char *>(&exri), sizeof(double));
 	  tfrfme.write(reinterpret_cast<char *>(&an), sizeof(double));