diff --git a/bin/fzf-tmux b/bin/fzf-tmux
index 6a18cf8ac22..3d93e6a948b 100755
--- a/bin/fzf-tmux
+++ b/bin/fzf-tmux
@@ -108,7 +108,7 @@ while [[ $# -gt 0 ]]; do
             max=$lines
           fi
           size=$(( max - size ))
-          [[ $size -lt 0 ]] && size=0
+          (( size < 0 )) && size=0
           opt="$opt -l $size"
         else
           opt="$opt -l $size"