--- a/devtools/server/actors/highlighters/css-grid.js
+++ b/devtools/server/actors/highlighters/css-grid.js
@@ -1156,17 +1156,21 @@ CssGridHighlighter.prototype = extend(Au
    */
   renderGridAreaOverlay() {
     let padding = 1;
 
     for (let i = 0; i < this.gridData.length; i++) {
       let fragment = this.gridData[i];
 
       for (let area of fragment.areas) {
-        let { rowStart, rowEnd, columnStart, columnEnd } = area;
+        let { rowStart, rowEnd, columnStart, columnEnd, type } = area;
+
+        if (type === "implicit") {
+          continue;
+        }
 
         // Draw the line edges for the grid area
         const areaColStart = fragment.cols.lines[columnStart - 1];
         const areaColEnd = fragment.cols.lines[columnEnd - 1];
 
         const areaRowStart = fragment.rows.lines[rowStart - 1];
         const areaRowEnd = fragment.rows.lines[rowEnd - 1];