diff --git a/lib/coverage.js b/lib/coverage.js
index <HASH>..<HASH> 100644
--- a/lib/coverage.js
+++ b/lib/coverage.js
@@ -37,7 +37,7 @@ function jscoverageFromIstanbulCoverage(coverage) {
     jscov[filename]['source'] = fs.readFileSync(file).toString().split('\n');
 
     for (var line = 0; line < jscov[filename]['source'].length; ++line) {
-      jscov[filename][line] = 0;
+      jscov[filename][line] = null;
     }
 
     for (var sid in coverage[file].s) {
Clean up coverage display for HTML reporter

Pro:
- HTML view of code coverage shows only lines that Istanbul actually
  instruments.

Con:
- This change alters the figures reported.  A <I>-line file with many
  comments, for example, may appear as though it only has <I> lines.