diff --git a/lib/libc/stdio/flags.c b/lib/libc/stdio/flags.c
index e1efe4e..3b21e52 100644
--- a/lib/libc/stdio/flags.c
+++ b/lib/libc/stdio/flags.c
@@ -76,11 +76,28 @@ __sflags(const char *mode, int *optr)
 		return (0);
 	}
 
-	/* [rwa]\+ or [rwa]b\+ means read and write */
-	if (*mode == '+' || (*mode == 'b' && mode[1] == '+')) {
-		ret = __SRW;
-		m = O_RDWR;
+	/* parse modifiers */
+	while (*mode) {
+		switch(*mode++) {
+		case '+':	/* rw mode */
+			ret = __SRW;
+			m = O_RDWR;
+			break;
+		case 'b':	/* binary mode */
+			/* no need for special treatment */
+			break;
+		case 'x':	/* force creation */
+			if ( (o & O_CREAT) && !(o & O_APPEND) ) {
+				o |= O_EXCL;
+				break;
+			}
+			/* fallthrough */
+		default:
+			errno = EINVAL;
+			return (0);
+		}
 	}
+
 	*optr = m | o;
 	return (ret);
 }
diff --git a/lib/libc/stdio/fopen.3 b/lib/libc/stdio/fopen.3
index a3a852f..dc727fb 100644
--- a/lib/libc/stdio/fopen.3
+++ b/lib/libc/stdio/fopen.3
@@ -73,10 +73,16 @@ The stream is positioned at the beginning of the file.
 .It Dq Li w
 Truncate to zero length or create text file for writing.
 The stream is positioned at the beginning of the file.
+.It Dq Li wx
+Create new file and open it for writing. It will fail if
+the file already exists.
 .It Dq Li w+
 Open for reading and writing.
 The file is created if it does not exist, otherwise it is truncated.
 The stream is positioned at the beginning of the file.
+.It Dq Li w+x
+Create new file and open it for reading and writing. It
+will fail if the file already exists.
 .It Dq Li a
 Open for writing.
 The file is created if it does not exist.
@@ -101,7 +107,7 @@ string can also include the letter ``b'' either as a third character or
 as a character between the characters in any of the two-character strings
 described above.
 This is strictly for compatibility with
-.St -isoC
+.St -isoC-2011
 and has no effect; the ``b'' is ignored.
 .Pp
 Any created files will have mode
@@ -276,7 +282,7 @@ and
 .Fn freopen
 functions
 conform to
-.St -isoC .
+.St -isoC-2011 .
 The
 .Fn fdopen
 function