diff --git a/lib/hcl-prv.h b/lib/hcl-prv.h
index 3db9d17..46dbeb2 100644
--- a/lib/hcl-prv.h
+++ b/lib/hcl-prv.h
@@ -581,6 +581,14 @@ struct hcl_flx_hi_t
 	hcl_oow_t char_count;
 };
 
+typedef struct hcl_flx_hb_t hcl_flx_hb_t; /* intermediate state for #b */
+struct hcl_flx_hb_t
+{
+	/* state data */
+	hcl_oow_t not_unused; /* for now */
+};
+
+
 typedef struct hcl_flx_hn_t hcl_flx_hn_t; /* hash-marked number - radixed number */
 struct hcl_flx_hn_t
 {
@@ -658,6 +666,7 @@ enum hcl_flx_state_t
 	HCL_FLX_COMMENT,
 	HCL_FLX_DELIM_TOKEN,
 	HCL_FLX_HMARKED_TOKEN,  /* hash-marked token */
+	HCL_FLX_HMARKED_B,      /* #b - intermediate state before #b[ or #b-radixed binary number */
 	HCL_FLX_HMARKED_CHAR,   /* hash-marked character that begins with #\ */
 	HCL_FLX_HMARKED_IDENT,  /* hash-marked identifier like #include, etc */
 	HCL_FLX_HMARKED_NUMBER, /* hash-marked number - radixed number like #xABCD */
@@ -750,6 +759,7 @@ struct hcl_compiler_t
 				hcl_flx_dt_t dt; /* delimiter token */
 				hcl_flx_hc_t hc; /* hash-marked character */
 				hcl_flx_hi_t hi; /* hash-marked identifier */
+				hcl_flx_hb_t hb; /* #b ... */
 				hcl_flx_hn_t hn; /* hash-marked number - radixed number */
 				hcl_flx_pi_t pi; /* plain identifier */
 				hcl_flx_pn_t pn; /* plain number */
diff --git a/lib/read.c b/lib/read.c
index 64455df..9474eed 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -1722,6 +1722,7 @@ static int feed_continue_with_char (hcl_t* hcl, hcl_ooci_t c, hcl_flx_state_t st
 #define FLX_DT(hcl) (&((hcl)->c->feed.lx.u.dt))
 #define FLX_HC(hcl) (&((hcl)->c->feed.lx.u.hc))
 #define FLX_HI(hcl) (&((hcl)->c->feed.lx.u.hi))
+#define FLX_HB(hcl) (&((hcl)->c->feed.lx.u.hb))
 #define FLX_HN(hcl) (&((hcl)->c->feed.lx.u.hn))
 #define FLX_PI(hcl) (&((hcl)->c->feed.lx.u.pi))
 #define FLX_PN(hcl) (&((hcl)->c->feed.lx.u.pn))
@@ -1739,6 +1740,11 @@ static HCL_INLINE void init_flx_hi (hcl_flx_hi_t* hi)
 	HCL_MEMSET (hi, 0, HCL_SIZEOF(*hi));
 }
 
+static HCL_INLINE void init_flx_hb (hcl_flx_hb_t* hb)
+{
+	HCL_MEMSET (hb, 0, HCL_SIZEOF(*hb));
+}
+
 static HCL_INLINE void init_flx_hn (hcl_flx_hn_t* hn, hcl_tok_type_t tok_type, hcl_synerrnum_t synerr_code, int radix)
 {
 	HCL_MEMSET (hn, 0, HCL_SIZEOF(*hn));
@@ -1987,8 +1993,15 @@ static int flx_hmarked_token (hcl_t* hcl, hcl_ooci_t c)
 			goto radixed_number;
 
 		case 'b':
+		#if 0
 			init_flx_hn (FLX_HN(hcl), HCL_TOK_RADNUMLIT, HCL_SYNERR_NUMLIT, 2);
 			goto radixed_number;
+		#else
+			/* if #b is followed by [, it is a starter for a byte array */
+			init_flx_hb (FLX_HB(hcl));
+			FEED_CONTINUE_WITH_CHAR (hcl, c, HCL_FLX_HMARKED_B);
+			break;
+		#endif
 
 		case 'e':
 			init_flx_hn (FLX_HN(hcl), HCL_TOK_ERRLIT, HCL_SYNERR_ERRLIT, 10);
@@ -2174,11 +2187,13 @@ not_consumed:
 
 static int flx_hmarked_b (hcl_t* hcl, hcl_ooci_t c)
 {
-#if 0
-	hcl_flx_hb_t* hb = FLX_HB(hcl);
+	/*hcl_flx_hb_t* hb = FLX_HB(hcl);*/
 
 	if (c == '[')
 	{
+		/* #b[ - byte array starter */
+		FEED_WRAP_UP_WITH_CHAR (hcl, c, HCL_TOK_BAPAREN);
+		goto consumed;
 	}
 	else
 	{
@@ -2186,7 +2201,6 @@ static int flx_hmarked_b (hcl_t* hcl, hcl_ooci_t c)
 		FEED_CONTINUE (hcl, HCL_FLX_HMARKED_NUMBER);
 		goto not_consumed;
 	}
-#endif
 
 consumed:
 	return 1;
@@ -2682,6 +2696,7 @@ static int feed_char (hcl_t* hcl, hcl_ooci_t c)
 		case HCL_FLX_COMMENT:          return flx_comment(hcl, c);
 		case HCL_FLX_DELIM_TOKEN:      return flx_delim_token(hcl, c);
 		case HCL_FLX_HMARKED_TOKEN:    return flx_hmarked_token(hcl, c);
+		case HCL_FLX_HMARKED_B:        return flx_hmarked_b(hcl, c);
 		case HCL_FLX_HMARKED_CHAR:     return flx_hmarked_char(hcl, c);
 		case HCL_FLX_HMARKED_IDENT:    return flx_hmarked_ident(hcl, c);
 		case HCL_FLX_HMARKED_NUMBER:   return flx_hmarked_number(hcl, c);
diff --git a/t/Makefile.am b/t/Makefile.am
index 5869246..cc54066 100644
--- a/t/Makefile.am
+++ b/t/Makefile.am
@@ -20,6 +20,7 @@ check_ERRORS = \
 	feed-5003.err \
 	feed-5004.err \
 	feed-5005.err \
+	feed-5006.err \
 	mlist-5001.err \
 	var-5001.err \
 	var-5002.err \
diff --git a/t/Makefile.in b/t/Makefile.in
index 2d6a627..4ec40f4 100644
--- a/t/Makefile.in
+++ b/t/Makefile.in
@@ -491,6 +491,7 @@ check_ERRORS = \
 	feed-5003.err \
 	feed-5004.err \
 	feed-5005.err \
+	feed-5006.err \
 	mlist-5001.err \
 	var-5001.err \
 	var-5002.err \
diff --git a/t/feed-5006.err b/t/feed-5006.err
new file mode 100644
index 0000000..e173b86
--- /dev/null
+++ b/t/feed-5006.err
@@ -0,0 +1,6 @@
+## #b can be followed by [ or binary digits.
+
+printf "%O\n" #b[ 10 20 30 ];
+printf "%010b\n" #b0101;
+printf "%O\n" #bxy; ##ERROR: syntax error - neither valid radixed number nor valid directive #bxy
+