diff --git a/README.md b/README.md
index e160331..2cfa7e0 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ The available commands are
 
 * `lyapunov`: to compute the Lyapunov exponents. This command prints
   ```
-  time instantaneous_lyapunov lyapunov
+  time index instantaneous_lyapunov lyapunov
   ```
   where `instantaneous_lyapunov` is computed from the tangent flow only between
   the given time and the previous one.
diff --git a/src/lyapunov.c b/src/lyapunov.c
index b041a83..7ff74f5 100644
--- a/src/lyapunov.c
+++ b/src/lyapunov.c
@@ -162,7 +162,7 @@ int lyapunov(
 
       // print
       for(i=0; i<MATSIZE; i++){
-	printf("% .15e % .15e % .15e\n",time, lyapunov[i], lyapunov_avg[i]);
+	printf("% .15e %3d % .15e % .15e\n",time, i, lyapunov[i], lyapunov_avg[i]);
       }
       printf("\n");
       fprintf(stderr,"% .15e\n",time);