diff --git a/disasm/isa_parser.cc b/disasm/isa_parser.cc
index 9bd19bf1..d6455146 100644
--- a/disasm/isa_parser.cc
+++ b/disasm/isa_parser.cc
@@ -347,6 +347,8 @@ isa_parser_t::isa_parser_t(const char* str, const char *priv)
     extension_table[EXT_ZBA] = true;
     extension_table[EXT_ZBB] = true;
     extension_table[EXT_ZBS] = true;
+  } else if (extension_table[EXT_ZBA] && extension_table[EXT_ZBB] && extension_table[EXT_ZBS]) {
+    extension_table['B'] = true;
   }
 
   if (extension_table['C']) {