diff --git a/src/ltlvisit/tostring.cc b/src/ltlvisit/tostring.cc
index 9e8198d30..d92887218 100644
--- a/src/ltlvisit/tostring.cc
+++ b/src/ltlvisit/tostring.cc
@@ -99,8 +99,8 @@ namespace spot
       };
 
       const char* spin_kw[] = {
-	"0",
-	"1",
+	"false", // 0 doesn't work from the command line
+	"true",  // 1 doesn't work from the command line
 	"[*0]",			// not supported
 	" xor ",		// rewritten
 	" -> ",			// rewritten, although supported