diff --git a/configure b/configure
index 9973d480b..a5ef9e8eb 100755
--- a/configure
+++ b/configure
@@ -3225,7 +3225,7 @@ if test "${enable_reserved_header_bits+set}" = set; then :
   0) :
     with_profinfo=false
       profinfo_width=0 ;; #(
-  [1-9]|1[0-9]|2[0-1]) :
+  [1-9]|[1-2][0-9]|3[0-1]) :
     with_profinfo=true
       profinfo_width="$enable_reserved_header_bits" ;; #(
   *) :
diff --git a/configure.ac b/configure.ac
index 0744dee22..c1e52891e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -311,7 +311,7 @@ AC_ARG_ENABLE([reserved-header-bits],
     [0],
       [with_profinfo=false
       profinfo_width=0],
-    [[[1-9]]|1[[0-9]]|2[[0-1]]],
+    [[[1-9]]|[[1-2]][[0-9]]|3[[0-1]]],
       [with_profinfo=true
       profinfo_width="$enable_reserved_header_bits"],
     [AC_MSG_ERROR([invalid argument to --enable-reserved-header-bits])])])