diff --git a/index.js b/index.js
index 3ebf3555..8cc70200 100755
--- a/index.js
+++ b/index.js
@@ -418,17 +418,19 @@ class NYC {
   }
 
   async getCoverageMapFromAllCoverageFiles (baseDirectory) {
-    const map = libCoverage.createCoverageMap({})
     const files = await this.coverageFiles(baseDirectory)
 
-    await pMap(
+    const reports = await pMap(
       files,
-      async f => {
-        const report = await this.coverageFileLoad(f, baseDirectory)
-        map.merge(report)
-      },
+      f => this.coverageFileLoad(f, baseDirectory),
       { concurrency: os.cpus().length }
     )
+    const map = reports.reduce((m, report) => {
+      m.merge(report)
+      return m
+    },
+    libCoverage.createCoverageMap({})
+    )
 
     map.data = await this.sourceMaps.remapCoverage(map.data)