diff --git a/scripts/php_extension_functions.txt b/scripts/php_extension_functions.txt
new file mode 100644
index 00000000..a503cbd4
--- /dev/null
+++ b/scripts/php_extension_functions.txt
@@ -0,0 +1,264 @@
+apc_add
+apc_bin_dump
+apc_bin_dumpfile
+apc_bin_load
+apc_bin_loadfile
+apc_cache_info
+apc_cas
+apc_clear_cache
+apc_compile_file
+apc_dec
+apc_define_constants
+apc_delete
+apc_delete_file
+apc_exists
+apc_fetch
+apc_inc
+apc_load_constants
+apc_sma_info
+apc_store
+bcadd
+bccomp
+bcdiv
+bcmod
+bcmul
+bcpow
+bcpowmod
+bcscale
+bcsqrt
+bcsub
+curl_close
+curl_copy_handle
+curl_errno
+curl_error
+curl_escape
+curl_exec
+curl_getinfo
+curl_init
+curl_multi_add_handle
+curl_multi_close
+curl_multi_exec
+curl_multi_getcontent
+curl_multi_info_read
+curl_multi_init
+curl_multi_remove_handle
+curl_multi_select
+curl_reset
+curl_setopt
+curl_setopt_array
+curl_share_close
+curl_share_init
+curl_share_setopt
+curl_unescape
+curl_version
+image2wbmp
+image_type_to_extension
+image_type_to_mime_type
+imagealphablending
+imageantialias
+imagearc
+imagechar
+imagecharup
+imagecolorallocate
+imagecolorallocatealpha
+imagecolorat
+imagecolorclosest
+imagecolorclosestalpha
+imagecolorclosesthwb
+imagecolordeallocate
+imagecolorexact
+imagecolorexactalpha
+imagecolormatch
+imagecolorresolve
+imagecolorresolvealpha
+imagecolorset
+imagecolorsforindex
+imagecolorstotal
+imagecolortransparent
+imageconvolution
+imagecopy
+imagecopymerge
+imagecopymergegray
+imagecopyresampled
+imagecopyresized
+imagecreate
+imagecreatefromgd
+imagecreatefromgd2
+imagecreatefromgd2part
+imagecreatefromgif
+imagecreatefromjpeg
+imagecreatefrompng
+imagecreatefromstring
+imagecreatefromwbmp
+imagecreatefromxbm
+imagecreatetruecolor
+imagedashedline
+imagedestroy
+imageellipse
+imagefill
+imagefilledarc
+imagefilledellipse
+imagefilledpolygon
+imagefilledrectangle
+imagefilltoborder
+imagefilter
+imagefontheight
+imagefontwidth
+imagegammacorrect
+imagegd
+imagegd2
+imagegif
+imageinterlace
+imageistruecolor
+imagejpeg
+imagelayereffect
+imageline
+imageloadfont
+imagepalettecopy
+imagepng
+imagepolygon
+imagerectangle
+imagerotate
+imagesavealpha
+imagesetbrush
+imagesetpixel
+imagesetstyle
+imagesetthickness
+imagesettile
+imagestring
+imagestringup
+imagesx
+imagesy
+imagetruecolortopalette
+imagetypes
+imagewbmp
+imagexbm
+ldap_connect
+ldap_close
+ldap_bind
+ldap_sasl_bind
+ldap_unbind
+ldap_read
+ldap_list
+ldap_search
+ldap_free_result
+ldap_count_entries
+ldap_first_entry
+ldap_next_entry
+ldap_get_entries
+ldap_first_attribute
+ldap_next_attribute
+ldap_get_attributes
+ldap_get_values
+ldap_get_values_len
+ldap_get_dn
+ldap_explode_dn
+ldap_dn2ufn
+ldap_add
+ldap_delete
+ldap_modify
+ldap_mod_add
+ldap_mod_replace
+ldap_mod_del
+ldap_errno
+ldap_err2str
+ldap_error
+ldap_compare
+ldap_sort
+ldap_rename
+ldap_get_option
+ldap_set_option
+ldap_first_reference
+ldap_next_reference
+ldap_parse_reference
+ldap_parse_result
+ldap_start_tls
+ldap_set_rebind_proc
+ldap_control_paged_result
+ldap_control_paged_result_response
+pcntl_fork
+pcntl_waitpid
+pcntl_wait
+pcntl_signal
+pcntl_signal_dispatch
+pcntl_wifexited
+pcntl_wifstopped
+pcntl_wifsignaled
+pcntl_wexitstatus
+pcntl_wtermsig
+pcntl_wstopsig
+pcntl_exec
+pcntl_alarm
+pcntl_get_last_error
+pcntl_errno
+pcntl_strerror
+pcntl_getpriority
+pcntl_setpriority
+pcntl_sigprocmask
+posix_kill
+posix_getpid
+posix_getppid
+posix_getuid
+posix_setuid
+posix_geteuid
+posix_seteuid
+posix_getgid
+posix_setgid
+posix_getegid
+posix_setegid
+posix_getgroups
+posix_getlogin
+posix_getpgrp
+posix_setsid
+posix_setpgid
+posix_getpgid
+posix_getsid
+posix_uname
+posix_times
+posix_ctermid
+posix_ttyname
+posix_isatty
+posix_getcwd
+posix_mkfifo
+posix_mknod
+posix_access
+posix_getgrnam
+posix_getgrgid
+posix_getpwnam
+posix_getpwuid
+posix_getrlimit
+posix_get_last_error
+posix_errno
+posix_strerror
+posix_initgroups
+socket_accept
+socket_bind
+socket_clear_error
+socket_close
+socket_connect
+socket_create
+socket_create_listen
+socket_create_pair
+socket_get_option
+socket_get_status
+socket_getopt
+socket_getpeername
+socket_getsockname
+socket_import_stream
+socket_last_error
+socket_listen
+socket_read
+socket_recv
+socket_recvfrom
+socket_select
+socket_send
+socket_sendto
+socket_set_block
+socket_set_blocking
+socket_set_nonblock
+socket_set_option
+socket_set_timeout
+socket_setopt
+socket_shutdown
+socket_strerror
+socket_write
diff --git a/scripts/phutil_symbols.php b/scripts/phutil_symbols.php
index 28253596..740ce680 100755
--- a/scripts/phutil_symbols.php
+++ b/scripts/phutil_symbols.php
@@ -415,6 +415,16 @@ function phutil_symbols_get_builtins() {
   $builtin_functions  = get_defined_functions();
   $builtin_functions  = $builtin_functions['internal'];
 
+  // Developers may not have every extension that a library potentially uses
+  // installed. We supplement the list of declared functions with a list of
+  // known extension functions to avoid raising false positives just because
+  // you don't have pcntl, etc.
+  $list = dirname(__FILE__).'/php_extension_functions.txt';
+  $extension_functions = file_get_contents($list);
+  $extension_functions = explode("\n", trim($extension_functions));
+
+  $builtin_functions = array_merge($builtin_functions, $extension_functions);
+
   return array(
     'class'     => array_fill_keys($builtin_classes, true) + array(
       'PhutilBootloader' => true,