diff --git a/src/core/core.tooltip.js b/src/core/core.tooltip.js
index cb21a9bc9..1b4687b0a 100644
--- a/src/core/core.tooltip.js
+++ b/src/core/core.tooltip.js
@@ -691,6 +691,7 @@ module.exports = function(Chart) {
 						ctx.fillRect(pt.x, pt.y, bodyFontSize, bodyFontSize);
 
 						// Border
+						ctx.lineWidth = 1;
 						ctx.strokeStyle = mergeOpacity(vm.labelColors[i].borderColor, opacity);
 						ctx.strokeRect(pt.x, pt.y, bodyFontSize, bodyFontSize);