diff --git a/src/KSPACE/pppm.cpp b/src/KSPACE/pppm.cpp
index 68b584b22e..d85e1ffa93 100644
--- a/src/KSPACE/pppm.cpp
+++ b/src/KSPACE/pppm.cpp
@@ -36,6 +36,8 @@
 
 using namespace LAMMPS_NS;
 
+#undef hz                      // required by IBM AIX compiler
+
 #define MAXORDER 7
 #define OFFSET 4096
 #define SMALL 0.00001