diff --git a/compat/plan9/head b/compat/plan9/head
new file mode 100755
index 0000000000..2840b2d50f
--- /dev/null
+++ b/compat/plan9/head
@@ -0,0 +1,10 @@
+#!/bin/sh
+
+n=10
+
+case "$1" in
+    -n)  n=$2;      shift 2 ;;
+    -n*) n=${1#-n}; shift   ;;
+esac
+
+exec sed ${n}q "$@"
diff --git a/compat/plan9/main.c b/compat/plan9/main.c
new file mode 100644
index 0000000000..d46f96d170
--- /dev/null
+++ b/compat/plan9/main.c
@@ -0,0 +1,34 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+int plan9_main(int argc, char **argv);
+
+#undef main
+int main(int argc, char **argv)
+{
+    /* The setfcr() function in lib9 is broken, must use asm. */
+#ifdef __i386
+    short fcr;
+    __asm__ volatile ("fstcw        %0 \n"
+                      "or      $63, %0 \n"
+                      "fldcw        %0 \n"
+                      : "=m"(fcr));
+#endif
+
+    return plan9_main(argc, argv);
+}
diff --git a/compat/plan9/printf b/compat/plan9/printf
new file mode 100755
index 0000000000..1a70a9e91a
--- /dev/null
+++ b/compat/plan9/printf
@@ -0,0 +1,2 @@
+#!/bin/sh
+exec awk "BEGIN { for (i = 2; i < ARGC; i++) printf \"$1\", ARGV[i] }" "$@"
diff --git a/configure b/configure
index 50a9d0216c..04a2ea3404 100755
--- a/configure
+++ b/configure
@@ -1071,7 +1071,7 @@ apply(){
 cp_if_changed(){
     cmp -s "$1" "$2" && echo "$2 is unchanged" && return
     mkdir -p "$(dirname $2)"
-    cp -f "$1" "$2"
+    $cp_f "$1" "$2"
 }
 
 # CONFIG_LIST contains configurable options, while HAVE_LIST is for
@@ -2010,6 +2010,7 @@ ar_default="ar"
 cc_default="gcc"
 cxx_default="g++"
 host_cc_default="gcc"
+cp_f="cp -f"
 install="install"
 ln_s="ln -sf"
 nm_default="nm -g"
@@ -3202,6 +3203,19 @@ case $target_os in
         ;;
     minix)
         ;;
+    plan9)
+        add_cppflags -D_C99_SNPRINTF_EXTENSION  \
+                     -D_REENTRANT_SOURCE        \
+                     -D_RESEARCH_SOURCE         \
+                     -DFD_SETSIZE=96            \
+                     -DHAVE_SOCK_OPTS
+        add_compat strtod.o strtod=avpriv_strtod
+        network_extralibs='-lbsd'
+        exeobjs=compat/plan9/main.o
+        disable ffserver
+        ln_s='ln -s -f'
+        cp_f='cp'
+        ;;
     none)
         ;;
     *)
@@ -3955,6 +3969,12 @@ elif enabled msvc; then
     enabled x86_32 && disable aligned_stack
 fi
 
+case $target_os in
+    plan9)
+        add_cppflags -Dmain=plan9_main
+    ;;
+esac
+
 enabled_any $THREADS_LIST      && enable threads
 
 enabled asm || { arch=c; disable $ARCH_LIST $ARCH_EXT_LIST; }
diff --git a/doc/platform.texi b/doc/platform.texi
index 68e23bf7c1..9da8bc88b1 100644
--- a/doc/platform.texi
+++ b/doc/platform.texi
@@ -304,4 +304,67 @@ and for a build with shared libraries
 ./configure --target-os=mingw32 --enable-shared --disable-static --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin
 @end example
 
+@chapter Plan 9
+
+The native @uref{http://plan9.bell-labs.com/plan9/, Plan 9} compiler
+does not implement all the C99 features needed by FFmpeg so the gcc
+port must be used.  Furthermore, a few items missing from the C
+library and shell environment need to be fixed.
+
+@itemize
+
+@item GNU awk, grep, make, and sed
+
+Working packages of these tools can be found at
+@uref{http://code.google.com/p/ports2plan9/downloads/list, ports2plan9}.
+They can be installed with @uref{http://9front.org/, 9front's} @code{pkg}
+utility by setting @code{pkgpath} to
+@code{http://ports2plan9.googlecode.com/files/}.
+
+@item Missing/broken @code{head} and @code{printf} commands
+
+Replacements adequate for building FFmpeg can be found in the
+@code{compat/plan9} directory.  Place these somewhere they will be
+found by the shell.  These are not full implementations of the
+commands and are @emph{not} suitable for general use.
+
+@item Missing C99 @code{stdint.h} and @code{inttypes.h}
+
+Replacement headers are available from
+@url{http://code.google.com/p/plan9front/issues/detail?id=152}.
+
+@item Missing or non-standard library functions
+
+Some functions in the C library are missing or incomplete.  The
+@code{@uref{http://ports2plan9.googlecode.com/files/gcc-apelibs-1207.tbz,
+gcc-apelibs-1207}} package from
+@uref{http://code.google.com/p/ports2plan9/downloads/list, ports2plan9}
+includes an updated C library, but installing the full package gives
+unusable executables.  Instead, keep the files from @code{gccbin.tgz}
+under @code{/386/lib/gnu}.  From the @code{libc.a} archive in the
+@code{gcc-apelibs-1207} package, extract the following object files and
+turn them into a library:
+
+@itemize
+@item @code{strerror.o}
+@item @code{strtoll.o}
+@item @code{snprintf.o}
+@item @code{vsnprintf.o}
+@item @code{vfprintf.o}
+@item @code{_IO_getc.o}
+@item @code{_IO_putc.o}
+@end itemize
+
+Use the @code{--extra-libs} option of @code{configure} to inform the
+build system of this library.
+
+@item FPU exceptions enabled by default
+
+Unlike most other systems, Plan 9 enables FPU exceptions by default.
+These must be disabled before calling any FFmpeg functions.  While the
+included tools will do this automatically, other users of the
+libraries must do it themselves.
+
+@end itemize
+
 @bye
diff --git a/libavformat/os_support.h b/libavformat/os_support.h
index 589eb7ee5e..b06cefd45e 100644
--- a/libavformat/os_support.h
+++ b/libavformat/os_support.h
@@ -67,7 +67,7 @@ static inline int is_dos_path(const char *path)
     return 0;
 }
 
-#if defined(__OS2__)
+#if defined(__OS2__) || defined(__Plan9__)
 #define SHUT_RD 0
 #define SHUT_WR 1
 #define SHUT_RDWR 2
diff --git a/libavformat/rtmppkt.h b/libavformat/rtmppkt.h
index 7ed31133c0..9b588031e7 100644
--- a/libavformat/rtmppkt.h
+++ b/libavformat/rtmppkt.h
@@ -253,7 +253,7 @@ int ff_amf_read_number(GetByteContext *gbc, double *val);
 /**
  * Read AMF string value.
  *
- * Appends a trailing \0 to output string in order to
+ * Appends a trailing null byte to output string in order to
  * ease later parsing.
  *
  *@param[in,out] gbc     GetByteContext initialized with AMF-formatted data