diff --git a/storage/memory/memory.go b/storage/memory/memory.go
index 500ec3e0..4af35c07 100644
--- a/storage/memory/memory.go
+++ b/storage/memory/memory.go
@@ -49,11 +49,18 @@ func (self *containerStorage) updatePrevStats(stats *info.ContainerStats) {
 	}
 	// make a deep copy.
 	self.prevStats.Timestamp = stats.Timestamp
+	// copy the slice first.
+	percpuSlice := self.prevStats.Cpu.Usage.PerCpu
 	*self.prevStats.Cpu = *stats.Cpu
-	self.prevStats.Cpu.Usage.PerCpu = make([]uint64, len(stats.Cpu.Usage.PerCpu))
-	for i, perCpu := range stats.Cpu.Usage.PerCpu {
-		self.prevStats.Cpu.Usage.PerCpu[i] = perCpu
+	// If the old slice is enough to hold the new data, then don't allocate
+	// a new slice.
+	if len(percpuSlice) != len(stats.Cpu.Usage.PerCpu) {
+		percpuSlice = make([]uint64, len(stats.Cpu.Usage.PerCpu))
 	}
+	for i, perCpu := range stats.Cpu.Usage.PerCpu {
+		percpuSlice[i] = perCpu
+	}
+	self.prevStats.Cpu.Usage.PerCpu = percpuSlice
 	*self.prevStats.Memory = *stats.Memory
 }
 
diff --git a/storage/test/storagetests.go b/storage/test/storagetests.go
index 87ae39f7..b27d9abf 100644
--- a/storage/test/storagetests.go
+++ b/storage/test/storagetests.go
@@ -44,6 +44,7 @@ func buildTrace(cpu, mem []uint64, duration time.Duration) []*info.ContainerStat
 		stats.Cpu.Usage.Total = cpuTotalUsage
 		stats.Cpu.Usage.User = stats.Cpu.Usage.Total
 		stats.Cpu.Usage.System = 0
+		stats.Cpu.Usage.PerCpu = []uint64{cpuUsage}
 
 		stats.Memory.Usage = mem[i]