diff --git a/lib/libc/iconv/_strtol.h b/lib/libc/iconv/_strtol.h
--- a/lib/libc/iconv/_strtol.h
+++ b/lib/libc/iconv/_strtol.h
@@ -91,6 +91,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = (c == '0' ? 8 : 10);
 
diff --git a/lib/libc/iconv/_strtoul.h b/lib/libc/iconv/_strtoul.h
--- a/lib/libc/iconv/_strtoul.h
+++ b/lib/libc/iconv/_strtoul.h
@@ -87,6 +87,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = (c == '0' ? 8 : 10);
 
diff --git a/lib/libc/locale/wcstoimax.c b/lib/libc/locale/wcstoimax.c
--- a/lib/libc/locale/wcstoimax.c
+++ b/lib/libc/locale/wcstoimax.c
@@ -86,6 +86,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == L'0' && (*s == L'b' || *s == L'B') &&
+	    (s[1] >= L'0' && s[1] <= L'1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == L'0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/locale/wcstol.c b/lib/libc/locale/wcstol.c
--- a/lib/libc/locale/wcstol.c
+++ b/lib/libc/locale/wcstol.c
@@ -80,6 +80,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == L'0' && (*s == L'b' || *s == L'B') &&
+	    (s[1] >= L'0' && s[1] <= L'1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == L'0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/locale/wcstoll.c b/lib/libc/locale/wcstoll.c
--- a/lib/libc/locale/wcstoll.c
+++ b/lib/libc/locale/wcstoll.c
@@ -86,6 +86,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == L'0' && (*s == L'b' || *s == L'B') &&
+	    (s[1] >= L'0' && s[1] <= L'1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == L'0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/locale/wcstoul.c b/lib/libc/locale/wcstoul.c
--- a/lib/libc/locale/wcstoul.c
+++ b/lib/libc/locale/wcstoul.c
@@ -80,6 +80,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == L'0' && (*s == L'b' || *s == L'B') &&
+	    (s[1] >= L'0' && s[1] <= L'1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == L'0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/locale/wcstoull.c b/lib/libc/locale/wcstoull.c
--- a/lib/libc/locale/wcstoull.c
+++ b/lib/libc/locale/wcstoull.c
@@ -86,6 +86,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == L'0' && (*s == L'b' || *s == L'B') &&
+	    (s[1] >= L'0' && s[1] <= L'1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == L'0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/locale/wcstoumax.c b/lib/libc/locale/wcstoumax.c
--- a/lib/libc/locale/wcstoumax.c
+++ b/lib/libc/locale/wcstoumax.c
@@ -86,6 +86,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == L'0' && (*s == L'b' || *s == L'B') &&
+	    (s[1] >= L'0' && s[1] <= L'1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == L'0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/stdio/printfcommon.h b/lib/libc/stdio/printfcommon.h
--- a/lib/libc/stdio/printfcommon.h
+++ b/lib/libc/stdio/printfcommon.h
@@ -194,6 +194,13 @@
 		} while (sval != 0);
 		break;
 
+	case 2:
+		do {
+			*--cp = to_char(val & 1);
+			val >>= 1;
+		} while (val);
+		break;
+
 	case 8:
 		do {
 			*--cp = to_char(val & 7);
@@ -244,6 +251,13 @@
 		} while (sval != 0);
 		break;
 
+	case 2:
+		do {
+			*--cp = to_char(val & 1);
+			val >>= 1;
+		} while (val);
+		break;
+
 	case 8:
 		do {
 			*--cp = to_char(val & 7);
diff --git a/lib/libc/stdio/vfprintf.c b/lib/libc/stdio/vfprintf.c
--- a/lib/libc/stdio/vfprintf.c
+++ b/lib/libc/stdio/vfprintf.c
@@ -613,6 +613,19 @@
 		case 'z':
 			flags |= SIZET;
 			goto rflag;
+		case 'B':
+		case 'b':
+			if (flags & INTMAX_SIZE)
+				ujval = UJARG();
+			else
+				ulval = UARG();
+			base = 2;
+			/* leading 0b/B only if non-zero */
+			if (flags & ALT &&
+			    (flags & INTMAX_SIZE ? ujval != 0 : ulval != 0))
+				ox[1] = ch;
+			goto nosign;
+			break;
 		case 'C':
 			flags |= LONGINT;
 			/*FALLTHROUGH*/
diff --git a/lib/libc/stdio/vfscanf.c b/lib/libc/stdio/vfscanf.c
--- a/lib/libc/stdio/vfscanf.c
+++ b/lib/libc/stdio/vfscanf.c
@@ -353,13 +353,21 @@
 				flags &= ~(SIGNOK|PFXOK|NDIGITS);
 			goto ok;
 
-		/* 1 through 7 always legal */
-		case '1': case '2': case '3':
-		case '4': case '5': case '6': case '7':
+		/* 1 always legal */
+		case '1':
 			base = basefix[base];
 			flags &= ~(SIGNOK | PFXOK | NDIGITS);
 			goto ok;
 
+		/* 2 through 7 ok iff octal, decimal, or hex */
+		case '2': case '3': case '4':
+		case '5': case '6': case '7':
+			base = basefix[base];
+			if (base <= 2)
+				break;	/* not legal here */
+			flags &= ~(SIGNOK | PFXOK | NDIGITS);
+			goto ok;
+
 		/* digits 8 and 9 ok iff decimal or hex */
 		case '8': case '9':
 			base = basefix[base];
@@ -368,10 +376,23 @@
 			flags &= ~(SIGNOK | PFXOK | NDIGITS);
 			goto ok;
 
+		/*
+		 * b ok iff flag still set & 2nd char (or 3rd char if
+		 * we have a sign).
+		 */
+		case 'b': case 'B':
+			if (flags & PFXOK && p ==
+			    buf + 1 + !!(flags & HAVESIGN)) {
+				base = 2;	/* if %i */
+				flags &= ~PFXOK;
+				goto ok;
+			}
+			/* FALLTHROUGH */
+
 		/* letters ok iff hex */
-		case 'A': case 'B': case 'C':
+		case 'A': case 'C':
 		case 'D': case 'E': case 'F':
-		case 'a': case 'b': case 'c':
+		case 'a': case 'c':
 		case 'd': case 'e': case 'f':
 			/* no need to fix base here */
 			if (base <= 10)
@@ -420,7 +441,7 @@
 	/*
 	 * If we had only a sign, it is no good; push back the sign.
 	 * If the number ends in `x', it was [sign] '0' 'x', so push
-	 * back the x and treat it as [sign] '0'.
+	 * back the x and treat it as [sign] '0'.  Same for `b'.
 	 */
 	if (flags & NDIGITS) {
 		if (p > buf)
@@ -428,7 +449,7 @@
 		return (0);
 	}
 	c = ((u_char *)p)[-1];
-	if (c == 'x' || c == 'X') {
+	if (c == 'x' || c == 'X' || c == 'b' || c == 'B') {
 		--p;
 		(void) __ungetc(c, fp);
 	}
@@ -554,6 +575,14 @@
 		/*
 		 * Conversions.
 		 */
+		case 'B':
+		case 'b':
+			flags |= PFXOK; /* enable 0b prefixing */
+			c = CT_INT;
+			flags |= UNSIGNED;
+			base = 2;
+			break;
+
 		case 'd':
 			c = CT_INT;
 			base = 10;
diff --git a/lib/libc/stdio/vfwprintf.c b/lib/libc/stdio/vfwprintf.c
--- a/lib/libc/stdio/vfwprintf.c
+++ b/lib/libc/stdio/vfwprintf.c
@@ -684,6 +684,19 @@
 		case 'z':
 			flags |= SIZET;
 			goto rflag;
+		case 'B':
+		case 'b':
+			if (flags & INTMAX_SIZE)
+				ujval = UJARG();
+			else
+				ulval = UARG();
+			base = 2;
+			/* leading 0b/B only if non-zero */
+			if (flags & ALT &&
+			    (flags & INTMAX_SIZE ? ujval != 0 : ulval != 0))
+				ox[1] = ch;
+			goto nosign;
+			break;
 		case 'C':
 			flags |= LONGINT;
 			/*FALLTHROUGH*/
diff --git a/lib/libc/stdio/vfwscanf.c b/lib/libc/stdio/vfwscanf.c
--- a/lib/libc/stdio/vfwscanf.c
+++ b/lib/libc/stdio/vfwscanf.c
@@ -336,13 +336,21 @@
 				flags &= ~(SIGNOK|PFXOK|NDIGITS);
 			goto ok;
 
-		/* 1 through 7 always legal */
-		case '1': case '2': case '3':
-		case '4': case '5': case '6': case '7':
+		/* 1 always legal */
+		case '1':
 			base = basefix[base];
 			flags &= ~(SIGNOK | PFXOK | NDIGITS);
 			goto ok;
 
+		/* 2 through 7 ok iff octal, decimal, or hex */
+		case '2': case '3': case '4':
+		case '5': case '6': case '7':
+			base = basefix[base];
+			if (base <= 2)
+				break;	/* not legal here */
+			flags &= ~(SIGNOK | PFXOK | NDIGITS);
+			goto ok;
+
 		/* digits 8 and 9 ok iff decimal or hex */
 		case '8': case '9':
 			base = basefix[base];
@@ -351,10 +359,23 @@
 			flags &= ~(SIGNOK | PFXOK | NDIGITS);
 			goto ok;
 
+		/*
+		 * b ok iff flag still set & 2nd char (or 3rd char if
+		 * we have a sign).
+		 */
+		case 'b':
+			if (flags & PFXOK && wcp ==
+			    buf + 1 + !!(flags & HAVESIGN)) {
+				base = 2;	/* if %i */
+				flags &= ~PFXOK;
+				goto ok;
+			}
+			/* FALLTHROUGH */
+
 		/* letters ok iff hex */
-		case 'A': case 'B': case 'C':
+		case 'A': case 'C':
 		case 'D': case 'E': case 'F':
-		case 'a': case 'b': case 'c':
+		case 'a': case 'c':
 		case 'd': case 'e': case 'f':
 			/* no need to fix base here */
 			if (base <= 10)
@@ -401,7 +422,7 @@
 	/*
 	 * If we had only a sign, it is no good; push back the sign.
 	 * If the number ends in `x', it was [sign] '0' 'x', so push
-	 * back the x and treat it as [sign] '0'.
+	 * back the x and treat it as [sign] '0'.  Same for `b'.
 	 */
 	if (flags & NDIGITS) {
 		if (wcp > buf)
@@ -409,7 +430,7 @@
 		return (0);
 	}
 	c = wcp[-1];
-	if (c == 'x' || c == 'X') {
+	if (c == 'x' || c == 'X' || c == 'b' || c == 'B') {
 		--wcp;
 		__ungetwc(c, fp, locale);
 	}
@@ -536,6 +557,14 @@
 		/*
 		 * Conversions.
 		 */
+		case 'B':
+		case 'b':
+			flags |= PFXOK; /* enable 0b prefixing */
+			c = CT_INT;
+			flags |= UNSIGNED;
+			base = 2;
+			break;
+
 		case 'd':
 			c = CT_INT;
 			base = 10;
diff --git a/lib/libc/stdlib/strtoimax.c b/lib/libc/stdlib/strtoimax.c
--- a/lib/libc/stdlib/strtoimax.c
+++ b/lib/libc/stdlib/strtoimax.c
@@ -87,6 +87,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == '0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/stdlib/strtol.c b/lib/libc/stdlib/strtol.c
--- a/lib/libc/stdlib/strtol.c
+++ b/lib/libc/stdlib/strtol.c
@@ -87,6 +87,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == '0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/stdlib/strtoll.c b/lib/libc/stdlib/strtoll.c
--- a/lib/libc/stdlib/strtoll.c
+++ b/lib/libc/stdlib/strtoll.c
@@ -63,8 +63,9 @@
 
 	/*
 	 * Skip white space and pick up leading +/- sign if any.
-	 * If base is 0, allow 0x for hex and 0 for octal, else
-	 * assume decimal; if base is already 16, allow 0x.
+	 * If base is 0, allow 0b for binary, 0x for hex, and 0 for
+	 * octal, else assume decimal; if base is already 2, allow
+	 * 0b; if base is already 16, allow 0x.
 	 */
 	s = nptr;
 	do {
@@ -87,6 +88,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == '0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/stdlib/strtoul.c b/lib/libc/stdlib/strtoul.c
--- a/lib/libc/stdlib/strtoul.c
+++ b/lib/libc/stdlib/strtoul.c
@@ -84,6 +84,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == '0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/stdlib/strtoull.c b/lib/libc/stdlib/strtoull.c
--- a/lib/libc/stdlib/strtoull.c
+++ b/lib/libc/stdlib/strtoull.c
@@ -85,6 +85,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == '0' ? 8 : 10;
 	acc = any = 0;
diff --git a/lib/libc/stdlib/strtoumax.c b/lib/libc/stdlib/strtoumax.c
--- a/lib/libc/stdlib/strtoumax.c
+++ b/lib/libc/stdlib/strtoumax.c
@@ -85,6 +85,13 @@
 		s += 2;
 		base = 16;
 	}
+	if ((base == 0 || base == 2) &&
+	    c == '0' && (*s == 'b' || *s == 'B') &&
+	    (s[1] >= '0' && s[1] <= '1')) {
+		c = s[1];
+		s += 2;
+		base = 2;
+	}
 	if (base == 0)
 		base = c == '0' ? 8 : 10;
 	acc = any = 0;