diff --git a/src/CodeCoverage/Report/HTML/Renderer/File.php b/src/CodeCoverage/Report/HTML/Renderer/File.php
index d52345d50..b340b4413 100644
--- a/src/CodeCoverage/Report/HTML/Renderer/File.php
+++ b/src/CodeCoverage/Report/HTML/Renderer/File.php
@@ -310,7 +310,7 @@ protected function renderSource(PHP_CodeCoverage_Report_Node_File $node)
             $popoverTitle   = '';
 
             if (array_key_exists($i, $coverageData)) {
-                $numTests = count($coverageData[$i]);
+                $numTests = isset($coverageData[$i]) ? count($coverageData[$i]) : 0;
 
                 if ($coverageData[$i] === null) {
                     $trClass = ' class="warning"';