diff --git a/PExpr.cc b/PExpr.cc
index 880dcc8c2..751d2be5f 100644
--- a/PExpr.cc
+++ b/PExpr.cc
@@ -20,6 +20,7 @@
 # include "config.h"
 
 # include  <iostream>
+# include  <cstring>
 
 # include  "PExpr.h"
 # include  "Module.h"
diff --git a/elab_pexpr.cc b/elab_pexpr.cc
index 59f80dd80..e4cdbe087 100644
--- a/elab_pexpr.cc
+++ b/elab_pexpr.cc
@@ -25,6 +25,7 @@
 # include  "netmisc.h"
 
 # include  <cstdlib>
+# include  <cstring>
 # include  <iostream>
 # include  "ivl_assert.h"
 
diff --git a/eval_tree.cc b/eval_tree.cc
index e50005fdf..7559c36ad 100644
--- a/eval_tree.cc
+++ b/eval_tree.cc
@@ -22,6 +22,7 @@
 
 # include  <iostream>
 # include  <cstdlib>
+# include  <cstring>
 # include  <math.h>
 
 # include  "netlist.h"
diff --git a/vvp/vvp.def b/vvp/vvp.def
index ad3990f05..1ec96567d 100644
--- a/vvp/vvp.def
+++ b/vvp/vvp.def
@@ -37,3 +37,4 @@ vpi_vprintf
 
 vpip_format_strength
 vpip_set_return_value
+vpip_calc_clog2