diff --git a/src/navier-stokes.c b/src/navier-stokes.c
index 3ae4ece..7b74a5f 100644
--- a/src/navier-stokes.c
+++ b/src/navier-stokes.c
@@ -235,6 +235,12 @@ int enstrophy(
       prevtime=time;
     }
 
+    // print alpha when it gets negative
+    if(alpha<0){
+      fprintf(stderr,"## negative alpha: % .8e at time % .8e\n",alpha, time);
+      printf("## negative alpha: % .15e at time % .15e\n",alpha, time);
+    }
+
     // get ready for next step
     step=next_step;