diff --git a/src/cellbase.h b/src/cellbase.h
--- a/src/cellbase.h
+++ b/src/cellbase.h
@@ -490,7 +490,8 @@ protected:
 ostream &operator<<(ostream &os, const CellBase &v);
 
 inline Vector PINdir(CellBase *here, CellBase *nb, Wall *w) {
-	return w->getTransporter( here, 1)  *  w->getInfluxVector(here);
+	  nb = NULL; // assignment merely to obviate compilation warning
+	  return w->getTransporter( here, 1)  *  w->getInfluxVector(here);
 }