Index: include/stdio.h
===================================================================
--- include/stdio.h
+++ include/stdio.h
@@ -302,7 +302,9 @@
 
 char	*ctermid(char *);
 FILE	*fdopen(int, const char *);
-int	 fileno(FILE *);
+#ifndef __FILENO_C
+static __inline int	 fileno(FILE *);
+#endif
 #endif /* __POSIX_VISIBLE */
 
 #if __POSIX_VISIBLE >= 199209
@@ -328,7 +330,9 @@
 void	 clearerr_unlocked(FILE *);
 int	 feof_unlocked(FILE *);
 int	 ferror_unlocked(FILE *);
-int	 fileno_unlocked(FILE *);
+#ifndef __FILENO_C
+static __inline int	 fileno_unlocked(FILE *);
+#endif
 #endif
 
 #if __POSIX_VISIBLE >= 200112
@@ -482,22 +486,44 @@
 
 extern int __isthreaded;
 
+#define	__sfileno(p)	((p)->_file)
+
+#if __POSIX_VISIBLE
+#ifndef __FILENO_C
+extern int __fileno_mt(FILE *fp);
+static __inline int
+fileno(FILE *p)
+{
+	return (!__isthreaded ? __sfileno(p) : (__fileno_mt)(p));
+}
+#endif
+#endif
+
+#if __BSD_VISIBLE
+/*
+ * See ISO/IEC 9945-1 ANSI/IEEE Std 1003.1 Second Edition 1996-07-12
+ * B.8.2.7 for the rationale behind the *_unlocked() macros.
+ */
+#ifndef __FILENO_C
+static __inline int
+fileno_unlocked(FILE *p)
+{
+	return __sfileno(p);
+}
+#endif
+#endif
+
 #ifndef __cplusplus
 
 #define	__sfeof(p)	(((p)->_flags & __SEOF) != 0)
 #define	__sferror(p)	(((p)->_flags & __SERR) != 0)
 #define	__sclearerr(p)	((void)((p)->_flags &= ~(__SERR|__SEOF)))
-#define	__sfileno(p)	((p)->_file)
 
 
 #define	feof(p)		(!__isthreaded ? __sfeof(p) : (feof)(p))
 #define	ferror(p)	(!__isthreaded ? __sferror(p) : (ferror)(p))
 #define	clearerr(p)	(!__isthreaded ? __sclearerr(p) : (clearerr)(p))
 
-#if __POSIX_VISIBLE
-#define	fileno(p)	(!__isthreaded ? __sfileno(p) : (fileno)(p))
-#endif
-
 #define	getc(fp)	(!__isthreaded ? __sgetc(fp) : (getc)(fp))
 #define	putc(x, fp)	(!__isthreaded ? __sputc(x, fp) : (putc)(x, fp))
 
@@ -512,7 +538,6 @@
 #define	feof_unlocked(p)	__sfeof(p)
 #define	ferror_unlocked(p)	__sferror(p)
 #define	clearerr_unlocked(p)	__sclearerr(p)
-#define	fileno_unlocked(p)	__sfileno(p)
 #endif
 #if __POSIX_VISIBLE >= 199506
 #define	getc_unlocked(fp)	__sgetc(fp)
Index: lib/libc/stdio/fileno.c
===================================================================
--- lib/libc/stdio/fileno.c
+++ lib/libc/stdio/fileno.c
@@ -37,6 +37,7 @@
 __FBSDID("$FreeBSD$");
 
 #include "namespace.h"
+#define __FILENO_C
 #include <stdio.h>
 #include "un-namespace.h"
 #include "libc_private.h"
@@ -56,6 +57,16 @@
 	return (fd);
 }
 
+/*
+ * wrapper for fileno() above, this is to be only used inside stdio.h static __inline fileno() wrapper
+ * to avoid symbol conflict for multithreaded programs (that causes infinite recursion).
+ */
+extern __inline int
+__fileno_mt(FILE *fp)
+{
+	return fileno(fp);
+}
+
 int
 fileno_unlocked(FILE *fp)
 {