diff --git a/async.cc b/async.cc
index 6029abd66..d1db2270c 100644
--- a/async.cc
+++ b/async.cc
@@ -23,12 +23,12 @@
 # include  "netlist.h"
 # include  <cassert>
 
-bool NetAssign::is_asynchronous() const
+bool NetAssign::is_asynchronous()
 {
       return true;
 }
 
-bool NetCondit::is_asynchronous() const
+bool NetCondit::is_asynchronous()
 {
       return false;
 }
diff --git a/netlist.h b/netlist.h
index dd773b25e..04ef95a06 100644
--- a/netlist.h
+++ b/netlist.h
@@ -2317,7 +2317,7 @@ class NetAssign : public NetAssignBase {
       explicit NetAssign(NetAssign_*lv, NetExpr*rv);
       ~NetAssign();
 
-      bool is_asynchronous() const;
+      bool is_asynchronous();
 
       virtual bool emit_proc(struct target_t*) const;
       virtual int match_proc(struct proc_match_t*);
@@ -2496,7 +2496,7 @@ class NetCondit  : public NetProc {
       virtual NexusSet* nex_input(bool rem_out = true);
       virtual void nex_output(NexusSet&o);
 
-      bool is_asynchronous() const;
+      bool is_asynchronous();
       bool synth_async(Design*des, NetScope*scope,
 		       const NetBus&nex_map, NetBus&nex_out);