diff --git a/mem/mem.go b/mem/mem.go
index e5a6b59a..47dbb13e 100644
--- a/mem/mem.go
+++ b/mem/mem.go
@@ -50,8 +50,8 @@ type VirtualMemoryStat struct {
 	// https://www.centos.org/docs/5/html/5.1/Deployment_Guide/s2-proc-meminfo.html
 	// https://www.kernel.org/doc/Documentation/filesystems/proc.txt
 	// https://www.kernel.org/doc/Documentation/vm/overcommit-accounting
-	ActiveFile     uint64 `json:activefile`
-	InactiveFile   uint64 `json:inactivefile`
+	ActiveFile     uint64 `json:"activefile"`
+	InactiveFile   uint64 `json:"inactivefile"`
 	Buffers        uint64 `json:"buffers"`
 	Cached         uint64 `json:"cached"`
 	Writeback      uint64 `json:"writeback"`
diff --git a/mem/mem_test.go b/mem/mem_test.go
index 0651a61c..fe3acfb6 100644
--- a/mem/mem_test.go
+++ b/mem/mem_test.go
@@ -71,7 +71,10 @@ func TestVirtualMemoryStat_String(t *testing.T) {
 		UsedPercent: 30.1,
 		Free:        40,
 	}
-	e := `{"total":10,"available":20,"used":30,"usedPercent":30.1,"free":40,"active":0,"inactive":0,"wired":0,"laundry":0,"buffers":0,"cached":0,"writeback":0,"dirty":0,"writebacktmp":0,"shared":0,"slab":0,"sreclaimable":0,"pagetables":0,"swapcached":0,"commitlimit":0,"committedas":0,"hightotal":0,"highfree":0,"lowtotal":0,"lowfree":0,"swaptotal":0,"swapfree":0,"mapped":0,"vmalloctotal":0,"vmallocused":0,"vmallocchunk":0,"hugepagestotal":0,"hugepagesfree":0,"hugepagesize":0}`
+	e := `{"total":10,"available":20,"used":30,"usedPercent":30.1,"free":40,"active":0,"inactive":0,"wired":0,"laundry":0,"activefile":0,"inactivefile":0,"buffers":0,"cached":0,"writeback":0,"dirty":0,"writebacktmp":0,"shared":0,"slab":0,"sreclaimable":0,"pagetables":0,"swapcached":0,"commitlimit":0,"committedas":0,"hightotal":0,"highfree":0,"lowtotal":0,"lowfree":0,"swaptotal":0,"swapfree":0,"mapped":0,"vmalloctotal":0,"vmallocused":0,"vmallocchunk":0,"hugepagestotal":0,"hugepagesfree":0,"hugepagesize":0}`
+
+	fmt.Println(v)
+	fmt.Println(e)
 	if e != fmt.Sprintf("%v", v) {
 		t.Errorf("VirtualMemoryStat string is invalid: %v", v)
 	}