diff --git a/runtime/syntax/tmux.vim b/runtime/syntax/tmux.vim
index 042b96e872..d2b31e874c 100644
--- a/runtime/syntax/tmux.vim
+++ b/runtime/syntax/tmux.vim
@@ -1,5 +1,5 @@
 " Language: tmux(1) configuration file
-" Version: 3.3-rc (git-964deae4)
+" Version: 3.3a (git-e7c829fc)
 " URL: https://github.com/ericpruitt/tmux.vim/
 " Maintainer: Eric Pruitt <eric.pruitt@gmail.com>
 " License: 2-Clause BSD (http://opensource.org/licenses/BSD-2-Clause)
@@ -17,8 +17,9 @@ let b:current_syntax = "tmux"
 syntax iskeyword @,48-57,_,192-255,-
 syntax case match
 
-syn keyword tmuxAction  none any current other
-syn keyword tmuxBoolean off on yes no
+" The values "yes" and "no" are synonyms for "on" and "off", so they do not
+" appear in the option table file.
+syn keyword tmuxEnums yes no
 
 syn keyword tmuxTodo FIXME NOTE TODO XXX contained
 
@@ -27,12 +28,20 @@ syn match tmuxKey               /\(C-\|M-\|\^\)\+\S\+/ display
 syn match tmuxNumber            /\<\d\+\>/             display
 syn match tmuxFlags             /\s-\a\+/              display
 syn match tmuxVariableExpansion /\$\({[A-Za-z_]\w*}\|[A-Za-z_]\w*\)/ display
-syn match tmuxControl           /^\s*%\(if\|elif\|else\|endif\)\>/
+syn match tmuxControl           /\(^\|\s\)%\(if\|elif\|else\|endif\)\($\|\s\)/ display
 syn match tmuxEscape            /\\\(u\x\{4\}\|U\x\{8\}\|\o\{3\}\|[\\ernt$]\)/ display
 
+" Missing closing bracket.
+syn match tmuxInvalidVariableExpansion /\${[^}]*$/ display
+" Starts with invalid character.
+syn match tmuxInvalidVariableExpansion /\${[^A-Za-z_][^}]*}/ display
+syn match tmuxInvalidVariableExpansion /\$[^A-Za-z_{ \t]/ display
+" Contains invalid character.
+syn match tmuxInvalidVariableExpansion /\${[^}]*[^A-Za-z0-9_][^}]*}/ display
+
 syn region tmuxComment start=/#/ skip=/\\\@<!\\$/ end=/$/ contains=tmuxTodo,@Spell
 
-syn region tmuxString start=+"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end='$' contains=tmuxFormatString,tmuxEscape,tmuxVariableExpansion,@Spell
+syn region tmuxString start=+"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end='$' contains=tmuxFormatString,tmuxEscape,tmuxVariableExpansion,tmuxInvalidVariableExpansion,@Spell
 syn region tmuxUninterpolatedString start=+'+ skip=+\\$+ excludenl end=+'+ end='$' contains=tmuxFormatString,@Spell
 
 " TODO: Figure out how escaping works inside of #(...) and #{...} blocks.
@@ -43,7 +52,7 @@ syn region tmuxFormatString start=/#(/ skip=/#(.\{-})/ end=/)/ contained keepend
 " At the time of this writing, the latest tmux release will parse a line
 " reading "abc=xyz set-option ..." as an assignment followed by a command
 " hence the presence of "\s" in the "end" argument.
-syn region tmuxAssignment matchgroup=tmuxVariable start=/^\s*[A-Za-z_]\w*=\@=/ skip=/\\$\|\\\s/ end=/\s\|$/ contains=tmuxString,tmuxUninterpolatedString,tmuxVariableExpansion,tmuxControl,tmuxEscape
+syn region tmuxAssignment matchgroup=tmuxVariable start=/^\s*[A-Za-z_]\w*=\@=/ skip=/\\$\|\\\s/ end=/\s\|$/ contains=tmuxString,tmuxUninterpolatedString,tmuxVariableExpansion,tmuxControl,tmuxEscape,tmuxInvalidVariableExpansion
 
 hi def link tmuxFormatString      Identifier
 hi def link tmuxAction            Boolean
@@ -51,8 +60,11 @@ hi def link tmuxBoolean           Boolean
 hi def link tmuxCommands          Keyword
 hi def link tmuxControl           PreCondit
 hi def link tmuxComment           Comment
+hi def link tmuxEnums             Boolean
 hi def link tmuxEscape            Special
 hi def link tmuxEscapeUnquoted    Special
+hi def link tmuxInvalidVariableExpansion
+\                                 Error
 hi def link tmuxKey               Special
 hi def link tmuxNumber            Number
 hi def link tmuxFlags             Identifier
@@ -77,78 +89,84 @@ endif
 
 syn keyword tmuxOptions
 \ activity-action after-bind-key after-capture-pane after-copy-mode
-\ after-display-message after-display-panes after-kill-pane
-\ after-list-buffers after-list-clients after-list-keys after-list-panes
-\ after-list-sessions after-list-windows after-load-buffer after-lock-server
-\ after-new-session after-new-window after-paste-buffer after-pipe-pane
-\ after-queue after-refresh-client after-rename-session after-rename-window
-\ after-resize-pane after-resize-window after-save-buffer
-\ after-select-layout after-select-pane after-select-window after-send-keys
-\ after-set-buffer after-set-environment after-set-hook after-set-option
-\ after-show-environment after-show-messages after-show-options
-\ after-split-window after-unbind-key aggressive-resize alert-activity
-\ alert-bell alert-silence allow-passthrough allow-rename alternate-screen
-\ assume-paste-time automatic-rename automatic-rename-format backspace
-\ base-index bell-action buffer-limit client-active client-attached
-\ client-detached client-focus-in client-focus-out client-resized
-\ client-session-changed clock-mode-colour clock-mode-style command-alias
-\ copy-command copy-mode-current-match-style copy-mode-mark-style
-\ copy-mode-match-style cursor-colour cursor-style default-command
-\ default-shell default-size default-terminal destroy-unattached
-\ detach-on-destroy display-panes-active-colour display-panes-colour
-\ display-panes-time display-time editor escape-time exit-empty
-\ exit-unattached extended-keys fill-character focus-events history-file
-\ history-limit key-table lock-after-time lock-command main-pane-height
-\ main-pane-width message-command-style message-limit message-style
-\ mode-keys mode-style monitor-activity monitor-bell monitor-silence mouse
-\ other-pane-height other-pane-width pane-active-border-style
-\ pane-base-index pane-border-format pane-border-indicators
-\ pane-border-lines pane-border-status pane-border-style pane-colours
-\ pane-died pane-exited pane-focus-in pane-focus-out pane-mode-changed
-\ pane-set-clipboard pane-title-changed popup-border-lines
+\ after-display-message after-display-panes after-kill-pane after-list-buffers
+\ after-list-clients after-list-keys after-list-panes after-list-sessions
+\ after-list-windows after-load-buffer after-lock-server after-new-session
+\ after-new-window after-paste-buffer after-pipe-pane after-queue
+\ after-refresh-client after-rename-session after-rename-window
+\ after-resize-pane after-resize-window after-save-buffer after-select-layout
+\ after-select-pane after-select-window after-send-keys after-set-buffer
+\ after-set-environment after-set-hook after-set-option after-show-environment
+\ after-show-messages after-show-options after-split-window after-unbind-key
+\ aggressive-resize alert-activity alert-bell alert-silence allow-passthrough
+\ allow-rename alternate-screen assume-paste-time automatic-rename
+\ automatic-rename-format backspace base-index bell-action buffer-limit
+\ client-active client-attached client-detached client-focus-in
+\ client-focus-out client-resized client-session-changed clock-mode-color
+\ clock-mode-colour clock-mode-style command-alias copy-command
+\ copy-mode-current-match-style copy-mode-mark-style copy-mode-match-style
+\ cursor-color cursor-colour cursor-style default-command default-shell
+\ default-size default-terminal destroy-unattached detach-on-destroy
+\ display-panes-active-color display-panes-active-colour display-panes-color
+\ display-panes-colour display-panes-time display-time editor escape-time
+\ exit-empty exit-unattached extended-keys fill-character focus-events
+\ history-file history-limit key-table lock-after-time lock-command
+\ main-pane-height main-pane-width menu-border-lines menu-border-style
+\ menu-selected-style menu-style message-command-style message-limit
+\ message-line message-style mode-keys mode-style monitor-activity monitor-bell
+\ monitor-silence mouse other-pane-height other-pane-width
+\ pane-active-border-style pane-base-index pane-border-format
+\ pane-border-indicators pane-border-lines pane-border-status pane-border-style
+\ pane-colors pane-colours pane-died pane-exited pane-focus-in pane-focus-out
+\ pane-mode-changed pane-set-clipboard pane-title-changed popup-border-lines
 \ popup-border-style popup-style prefix prefix2 prompt-history-limit
 \ remain-on-exit remain-on-exit-format renumber-windows repeat-time
 \ scroll-on-clear session-closed session-created session-renamed
 \ session-window-changed set-clipboard set-titles set-titles-string
 \ silence-action status status-bg status-fg status-format status-interval
-\ status-justify status-keys status-left status-left-length
-\ status-left-style status-position status-right status-right-length
-\ status-right-style status-style synchronize-panes terminal-features
-\ terminal-overrides update-environment user-keys visual-activity
-\ visual-bell visual-silence window-active-style window-layout-changed
-\ window-linked window-pane-changed window-renamed window-resized
-\ window-size window-status-activity-style window-status-bell-style
-\ window-status-current-format window-status-current-style
-\ window-status-format window-status-last-style window-status-separator
-\ window-status-style window-style window-unlinked word-separators
-\ wrap-search xterm-keys
+\ status-justify status-keys status-left status-left-length status-left-style
+\ status-position status-right status-right-length status-right-style
+\ status-style synchronize-panes terminal-features terminal-overrides
+\ update-environment user-keys visual-activity visual-bell visual-silence
+\ window-active-style window-layout-changed window-linked window-pane-changed
+\ window-renamed window-resized window-size window-status-activity-style
+\ window-status-bell-style window-status-current-format
+\ window-status-current-style window-status-format window-status-last-style
+\ window-status-separator window-status-style window-style window-unlinked
+\ word-separators wrap-search xterm-keys
 
 syn keyword tmuxCommands
-\ attach attach-session bind bind-key break-pane breakp capture-pane
-\ capturep choose-buffer choose-client choose-session choose-tree
-\ choose-window clear-history clear-prompt-history clearhist clearphist
-\ clock-mode command-prompt confirm confirm-before copy-mode customize-mode
-\ delete-buffer deleteb detach detach-client display display-menu
-\ display-message display-panes display-popup displayp find-window findw has
-\ has-session if if-shell info join-pane joinp kill-pane kill-server
-\ kill-session kill-window killp killw last last-pane last-window lastp
-\ link-window linkw list-buffers list-clients list-commands list-keys
-\ list-panes list-sessions list-windows load-buffer loadb lock lock-client
-\ lock-server lock-session lockc locks ls lsb lsc lscm lsk lsp lsw menu
-\ move-pane move-window movep movew new new-session new-window neww next
-\ next-layout next-window nextl paste-buffer pasteb pipe-pane pipep popup
-\ prev previous-layout previous-window prevl refresh refresh-client rename
-\ rename-session rename-window renamew resize-pane resize-window resizep
-\ resizew respawn-pane respawn-window respawnp respawnw rotate-window
-\ rotatew run run-shell save-buffer saveb select-layout select-pane
-\ select-window selectl selectp selectw send send-keys send-prefix
-\ server-info set set-buffer set-environment set-hook set-option
-\ set-window-option setb setenv setw show show-buffer show-environment
-\ show-hooks show-messages show-options show-prompt-history
-\ show-window-options showb showenv showmsgs showphist showw source
-\ source-file split-pane split-window splitp splitw start start-server
-\ suspend-client suspendc swap-pane swap-window swapp swapw switch-client
-\ switchc unbind unbind-key unlink-window unlinkw wait wait-for
+\ attach attach-session bind bind-key break-pane breakp capture-pane capturep
+\ choose-buffer choose-client choose-session choose-tree choose-window
+\ clear-history clear-prompt-history clearhist clearphist clock-mode
+\ command-prompt confirm confirm-before copy-mode customize-mode delete-buffer
+\ deleteb detach detach-client display display-menu display-message
+\ display-panes display-popup displayp find-window findw has has-session if
+\ if-shell info join-pane joinp kill-pane kill-server kill-session kill-window
+\ killp killw last last-pane last-window lastp link-window linkw list-buffers
+\ list-clients list-commands list-keys list-panes list-sessions list-windows
+\ load-buffer loadb lock lock-client lock-server lock-session lockc locks ls
+\ lsb lsc lscm lsk lsp lsw menu move-pane move-window movep movew new
+\ new-session new-window neww next next-layout next-window nextl paste-buffer
+\ pasteb pipe-pane pipep popup prev previous-layout previous-window prevl
+\ refresh refresh-client rename rename-session rename-window renamew
+\ resize-pane resize-window resizep resizew respawn-pane respawn-window
+\ respawnp respawnw rotate-window rotatew run run-shell save-buffer saveb
+\ select-layout select-pane select-window selectl selectp selectw send
+\ send-keys send-prefix server-access server-info set set-buffer
+\ set-environment set-hook set-option set-window-option setb setenv setw show
+\ show-buffer show-environment show-hooks show-messages show-options
+\ show-prompt-history show-window-options showb showenv showmsgs showphist
+\ showw source source-file split-pane split-window splitp splitw start
+\ start-server suspend-client suspendc swap-pane swap-window swapp swapw
+\ switch-client switchc unbind unbind-key unlink-window unlinkw wait wait-for
+
+syn keyword tmuxEnums
+\ absolute-centre all always any arrows bar blinking-bar blinking-block
+\ blinking-underline block both bottom centre color colour current default
+\ double emacs external failed heavy largest latest left manual next
+\ no-detached none number off on other padded previous right rounded simple
+\ single smallest top underline vi
 
 let &cpo = s:original_cpo
 unlet! s:original_cpo s:bg s:i