diff --git a/powerline/bindings/bash/powerline.sh b/powerline/bindings/bash/powerline.sh
index c5d56e7c..4aeefea6 100644
--- a/powerline/bindings/bash/powerline.sh
+++ b/powerline/bindings/bash/powerline.sh
@@ -10,8 +10,7 @@ if test -z "${POWERLINE_COMMAND}" ; then
 fi
 
 _powerline_init_tmux_support() {
-	# Note: `test -w ""` returns false, so first condition may be removed
-	if test -n "$TMUX" && test -w "$TMUX" ; then
+	if test -n "$TMUX" && tmux source-file /dev/null &>/dev/null ; then
 		# TMUX variable may be unset to create new tmux session inside this one
 		_POWERLINE_TMUX="$TMUX"
 
diff --git a/powerline/bindings/fish/powerline-setup.fish b/powerline/bindings/fish/powerline-setup.fish
index 75ca19c4..71acb3cb 100644
--- a/powerline/bindings/fish/powerline-setup.fish
+++ b/powerline/bindings/fish/powerline-setup.fish
@@ -20,18 +20,20 @@ function powerline-setup
 		"
 	end
 	_powerline_update
-	if test -w "$TMUX"
-		function _powerline_tmux_setenv
-			tmux setenv -g TMUX_$argv[1]_(tmux display -p "#D" | tr -d "%") "$argv[2]"
-			tmux refresh -S
+	if test -n "$TMUX"
+		if tmux source-file /dev/null ^/dev/null
+			function _powerline_tmux_setenv
+				tmux setenv -g TMUX_$argv[1]_(tmux display -p "#D" | tr -d "%") "$argv[2]"
+				tmux refresh -S
+			end
+			function --on-variable PWD _powerline_tmux_set_pwd
+				_powerline_tmux_setenv PWD "$PWD"
+			end
+			function --on-signal WINCH _powerline_tmux_set_columns
+				_powerline_tmux_setenv COLUMNS "$COLUMNS"
+			end
+			_powerline_tmux_set_columns
+			_powerline_tmux_set_pwd
 		end
-		function --on-variable PWD _powerline_tmux_set_pwd
-			_powerline_tmux_setenv PWD "$PWD"
-		end
-		function --on-signal WINCH _powerline_tmux_set_columns
-			_powerline_tmux_setenv COLUMNS "$COLUMNS"
-		end
-		_powerline_tmux_set_columns
-		_powerline_tmux_set_pwd
 	end
 end
diff --git a/powerline/bindings/tcsh/powerline.tcsh b/powerline/bindings/tcsh/powerline.tcsh
index 44f969b6..b83498ad 100644
--- a/powerline/bindings/tcsh/powerline.tcsh
+++ b/powerline/bindings/tcsh/powerline.tcsh
@@ -14,7 +14,7 @@ if ! $?POWERLINE_COMMAND then
 		setenv POWERLINE_COMMAND $POWERLINE_SOURCED:h:h:h:h:q/scripts/powerline
 	endif
 endif
-alias _powerline_tmux_set_pwd 'if ( $?TMUX && { test -w $TMUX:q } ) tmux setenv -g TMUX_PWD_`tmux display -p "#D" | tr -d %` $PWD:q ; if ( $?TMUX && { test -w $TMUX:q } ) tmux refresh -S'
+alias _powerline_tmux_set_pwd 'if ( $?TMUX && { tmux source-file /dev/null >&/dev/null } ) tmux setenv -g TMUX_PWD_`tmux display -p "#D" | tr -d %` $PWD:q ; if ( $?TMUX && { tmux source-file /dev/null >&/dev/null } ) tmux refresh -S'
 alias _powerline_set_prompt 'set prompt="`$POWERLINE_COMMAND shell left -r tcsh_prompt --last_exit_code=$?`"'
 alias _powerline_set_rprompt 'set rprompt="`$POWERLINE_COMMAND shell right -r tcsh_prompt --last_exit_code=$?` "'
 alias cwdcmd "`alias cwdcmd` ; _powerline_tmux_set_pwd"
diff --git a/powerline/bindings/zsh/powerline.zsh b/powerline/bindings/zsh/powerline.zsh
index 6e8206fe..46123940 100644
--- a/powerline/bindings/zsh/powerline.zsh
+++ b/powerline/bindings/zsh/powerline.zsh
@@ -12,8 +12,7 @@ integer _POWERLINE_JOBNUM
 
 _powerline_init_tmux_support() {
 	emulate -L zsh
-	# Note: `test -w ""` returns false, so first condition may be removed
-	if test -n "$TMUX" && test -w "$TMUX" ; then
+	if test -n "$TMUX" && tmux source-file /dev/null &>/dev/null ; then
 		# TMUX variable may be unset to create new tmux session inside this one
 		typeset -g _POWERLINE_TMUX="$TMUX"