--- a/devtools/server/actors/highlighters/css-grid.js
+++ b/devtools/server/actors/highlighters/css-grid.js
@@ -836,20 +836,21 @@ class CssGridHighlighter extends AutoRef
     this.ctx.textBaseline = "middle";
 
     // Draw the text for the grid area name.
     for (let rowNumber = rowStart; rowNumber < rowEnd; rowNumber++) {
       for (let columnNumber = columnStart; columnNumber < columnEnd; columnNumber++) {
         let row = fragment.rows.tracks[rowNumber - 1];
         let column = fragment.cols.tracks[columnNumber - 1];
 
-        // Check if the font size is exceeds the bounds of the containing grid cell.
+        // If the font size exceeds the bounds of the containing grid cell, size it its
+        // row or column dimension, whichever is smallest.
         if (fontSize > (column.breadth * displayPixelRatio) ||
             fontSize > (row.breadth * displayPixelRatio)) {
-          fontSize = (column.breadth + row.breadth) / 2;
+          fontSize = Math.min([column.breadth, row.breadth]);
           this.ctx.font = fontSize + "px " + GRID_FONT_FAMILY;
         }
 
         let textWidth = this.ctx.measureText(area.name).width;
         // The width of the character 'm' approximates the height of the text.
         let textHeight = this.ctx.measureText("m").width;
         // Padding in pixels for the line number text inside of the line number container.
         let padding = 3 * displayPixelRatio;