diff --git a/main.cc b/main.cc
index 3ba8774f1..79a88e40c 100644
--- a/main.cc
+++ b/main.cc
@@ -714,6 +714,9 @@ int main(int argc, char*argv[])
 	    cout << endl << "PARSING INPUT" << endl;
       }
 
+      const char *flag_dvp = flags["DISABLE_VIRTUAL_PINS"];
+      if (flag_dvp) disable_virtual_pins = strcmp(flag_dvp,"true")==0;
+
 	/* Parse the input. Make the pform. */
       int rc = pform_parse(argv[optind]);
 
diff --git a/netlist.cc b/netlist.cc
index df701a338..a3106e796 100644
--- a/netlist.cc
+++ b/netlist.cc
@@ -226,6 +226,11 @@ Link& NetPins::pin(unsigned idx)
 
 const Link& NetPins::pin(unsigned idx) const
 {
+      if (!pins_ && !disable_virtual_pins) {
+	    cerr << get_fileline() << ": internal error: pin is unexpectedly"
+	      " virtual, try again with -pDISABLE_VIRTUAL_PINS=true" << endl;
+	    assert(NULL);
+      }
       assert(pins_);
       assert(idx < npins_);
       assert(idx == 0? pins_[0].pin_zero_ : pins_[idx].pin_==idx);