diff --git a/NEWS b/NEWS
index 75598ce7a..941c0b2f6 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,8 @@ New in spot 1.99.2a (not yet released)
   * Bugs fixed
     - Some acceptance conditions like Fin(0)|Fin(1)|Fin(2)&Inf(3)
       where not detected as generalized-Rabin.
+    - Unknown arguments for print_hoa() (i.e., option -H in command-line
+      tools) are now diagnosed.
 
 New in spot 1.99.2 (2015-07-18)
 
diff --git a/src/tests/readsave.test b/src/tests/readsave.test
index 883bb7c11..9c562935e 100755
--- a/src/tests/readsave.test
+++ b/src/tests/readsave.test
@@ -696,3 +696,7 @@ State: 2
 EOF
 
 diff output3 expect3
+
+
+$autfilt -Hk input 2>stderr && exit 1
+grep 'print_hoa.*k' stderr
diff --git a/src/twaalgos/dot.cc b/src/twaalgos/dot.cc
index 21e39577e..02053754b 100644
--- a/src/twaalgos/dot.cc
+++ b/src/twaalgos/dot.cc
@@ -173,7 +173,7 @@ namespace spot
 	      break;
 	    default:
 	      throw std::runtime_error
-		(std::string("unknown option for dotty(): ") + c);
+		(std::string("unknown option for print_dot(): ") + c);
 	    }
       }
 
diff --git a/src/twaalgos/hoa.cc b/src/twaalgos/hoa.cc
index 39d511563..208340232 100644
--- a/src/twaalgos/hoa.cc
+++ b/src/twaalgos/hoa.cc
@@ -247,7 +247,7 @@ namespace spot
     if (opt)
       while (*opt)
 	{
-	  switch (*opt++)
+	  switch (char c = *opt++)
 	    {
 	    case 'i':
 	      implicit_labels = true;
@@ -264,6 +264,9 @@ namespace spot
 	    case 't':
 	      acceptance = Hoa_Acceptance_Transitions;
 	      break;
+	    default:
+	      throw std::runtime_error
+		(std::string("unknown option for print_hoa(): ") + c);
 	    }
 	}
 
diff --git a/src/twaalgos/neverclaim.cc b/src/twaalgos/neverclaim.cc
index 06b94b822..9580ebb0d 100644
--- a/src/twaalgos/neverclaim.cc
+++ b/src/twaalgos/neverclaim.cc
@@ -61,7 +61,8 @@ namespace spot
 		break;
 	      default:
 		throw std::runtime_error
-		  (std::string("unknown option for never_claim(): ") + c);
+		  (std::string("unknown option for print_never_claim(): ")
+		   + c);
 	      }
       }