diff --git a/libc/stdio/printf_common.h b/libc/stdio/printf_common.h
index 4dc5ca1..e761835 100644
--- a/libc/stdio/printf_common.h
+++ b/libc/stdio/printf_common.h
@@ -524,6 +524,8 @@
       case 'u':
       case 'X':
       case 'x':
+      case 'B':
+      case 'b':
         ADDUARG();
         break;
       default: /* "%?" prints ?, unless ? is NUL */