diff --git a/bin/picom-trans b/bin/picom-trans
index 6b1d1df..331487c 100755
--- a/bin/picom-trans
+++ b/bin/picom-trans
@@ -160,7 +160,7 @@ else
   fi
 
   # Find the line number of the target window in the window tree
-  lineno=$(echo -n "$treeout" | grep -nw "$wid" | head -n1 | cut -d ':' -f 1)
+  lineno=$(echo -n "$treeout" | grep -nw "^\s*$wid" | head -n1 | cut -d ':' -f 1)
 
   if test -z "$lineno"; then
     echo 'Failed to find window in window tree.'
@@ -169,7 +169,7 @@ else
 
   # Find the highest ancestor of the target window below
   topmost=$(echo -n "$treeout" \
-    | head -n $((lineno + 1)) \
+    | head -n $lineno \
     | sed -n 's/^     \(0x[[:xdigit:]]*\).*/\1/p' \
     | tail -n 1)
 fi