diff --git a/src/message.c b/src/message.c
index 513f288..a7398f6 100644
--- a/src/message.c
+++ b/src/message.c
@@ -4091,12 +4091,14 @@
 	    char    length_modifier = '\0';
 
 	    /* temporary buffer for simple numeric->string conversion */
-# ifdef FEAT_FLOAT
+# if defined(FEAT_FLOAT)
 #  define TMP_LEN 350	/* On my system 1e308 is the biggest number possible.
 			 * That sounds reasonable to use as the maximum
 			 * printable. */
+# elif defined(FEAT_NUM64)
+#  define TMP_LEN 66
 # else
-#  define TMP_LEN 32
+#  define TMP_LEN 34
 # endif
 	    char    tmp[TMP_LEN];
 
@@ -4343,9 +4345,13 @@
 		}
 		break;
 
-	    case 'd': case 'u': case 'o': case 'x': case 'X': case 'p':
+	    case 'd': case 'u':
+	    case 'b': case 'B':
+	    case 'o':
+	    case 'x': case 'X':
+	    case 'p':
 		{
-		    /* NOTE: the u, o, x, X and p conversion specifiers
+		    /* NOTE: the u, b, o, x, X and p conversion specifiers
 		     * imply the value is unsigned;  d implies a signed
 		     * value */
 
@@ -4370,6 +4376,9 @@
 		    uvarnumber_T ullong_arg = 0;
 # endif
 
+		    /* only defined for b convertion */
+		    uvarnumber_T bin_arg = 0;
+
 		    /* pointer argument value -only defined for p
 		     * conversion */
 		    void *ptr_arg = NULL;
@@ -4386,6 +4395,17 @@
 			if (ptr_arg != NULL)
 			    arg_sign = 1;
 		    }
+		    else if (fmt_spec == 'b' || fmt_spec == 'B')
+		    {
+			bin_arg =
+# if defined(FEAT_EVAL)
+				    tvs != NULL ?
+					   (uvarnumber_T)tv_nr(tvs, &arg_idx) :
+# endif
+					va_arg(ap, uvarnumber_T);
+			if (bin_arg != 0)
+			    arg_sign = 1;
+		    }
 		    else if (fmt_spec == 'd')
 		    {
 			/* signed */
@@ -4492,7 +4512,8 @@
 		    else if (alternate_form)
 		    {
 			if (arg_sign != 0
-				     && (fmt_spec == 'x' || fmt_spec == 'X') )
+				     && (fmt_spec == 'b' || fmt_spec == 'B'
+				      || fmt_spec == 'x' || fmt_spec == 'X') )
 			{
 			    tmp[str_arg_l++] = '0';
 			    tmp[str_arg_l++] = fmt_spec;
@@ -4508,7 +4529,7 @@
 		    {
 			/* When zero value is formatted with an explicit
 			 * precision 0, the resulting formatted string is
-			 * empty (d, i, u, o, x, X, p).   */
+			 * empty (d, i, u, b, B, o, x, X, p).   */
 		    }
 		    else
 		    {
@@ -4541,6 +4562,22 @@
 
 			if (fmt_spec == 'p')
 			    str_arg_l += sprintf(tmp + str_arg_l, f, ptr_arg);
+			else if (fmt_spec == 'b' || fmt_spec == 'B')
+			{
+			    char	    b[8 * sizeof(uvarnumber_T)];
+			    size_t	    b_l = 0;
+			    uvarnumber_T    bn = bin_arg;
+
+			    do
+			    {
+				b[sizeof(b) - ++b_l] = '0' + (bn & 0x1);
+				bn >>= 1;
+			    }
+			    while (bn != 0);
+
+			    memcpy(tmp + str_arg_l, b + sizeof(b) - b_l, b_l);
+			    str_arg_l += b_l;
+			}
 			else if (fmt_spec == 'd')
 			{
 			    /* signed */