diff --git a/tsdb/engine/tsm1/cache.go b/tsdb/engine/tsm1/cache.go
index d1f97b1c36..a4dcc8f043 100644
--- a/tsdb/engine/tsm1/cache.go
+++ b/tsdb/engine/tsm1/cache.go
@@ -71,6 +71,11 @@ func (e *entry) add(values []Value) error {
 		needSort bool
 	)
 
+	if len(values) == 0 {
+		return nil // Nothing to do.
+	}
+
+	// Are any of the new values out of order?
 	for _, v := range values {
 		if v.UnixNano() <= prevTime {
 			needSort = true
@@ -79,30 +84,42 @@ func (e *entry) add(values []Value) error {
 		prevTime = v.UnixNano()
 	}
 
-	// if there are existing values make sure they're all less than the first of
-	// the new values being added
-	e.mu.Lock()
-	if needSort {
-		e.needSort = needSort
-	}
+	// entry currently has no values, so add the new ones and we're done.
 	if len(e.values) == 0 {
+		e.mu.Lock()
+		// Do the values need sorting?
+		if needSort {
+			e.needSort = needSort
+		}
 		e.values = values
-	} else {
-		// Make sure the new values are the same type as the exiting values
-		et := valueType(e.values[0])
-		for _, v := range values {
-			if et != valueType(v) {
-				e.mu.Unlock()
-				return tsdb.ErrFieldTypeConflict
-			}
-		}
-		l := len(e.values)
-		lastValTime := e.values[l-1].UnixNano()
-		if lastValTime >= values[0].UnixNano() {
-			e.needSort = true
-		}
-		e.values = append(e.values, values...)
+		e.mu.Unlock()
+		return nil
 	}
+
+	e.mu.RLock()
+	// What's the type of the values in the entry?
+	vtype := valueType(e.values[0])
+	// Are the new values occuring after the existing ones?
+	if !needSort && e.values[len(e.values)-1].UnixNano() >= values[0].UnixNano() {
+		needSort = true
+	}
+	e.mu.RUnlock()
+
+	// Make sure the new values are the same type as the exiting values.
+	for _, v := range values {
+		if vtype != valueType(v) {
+			return tsdb.ErrFieldTypeConflict
+		}
+	}
+
+	// Append the new values to the existing ones...
+
+	e.mu.Lock()
+	// Do the values need sorting?
+	if needSort {
+		e.needSort = true
+	}
+	e.values = append(e.values, values...)
 	e.mu.Unlock()
 	return nil
 }
diff --git a/tsdb/engine/tsm1/cache_test.go b/tsdb/engine/tsm1/cache_test.go
index 99e09c8ea1..2a962a0871 100644
--- a/tsdb/engine/tsm1/cache_test.go
+++ b/tsdb/engine/tsm1/cache_test.go
@@ -741,3 +741,30 @@ func BenchmarkCacheParallelFloatEntries(b *testing.B) {
 		}
 	})
 }
+
+func BenchmarkEntry_add(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			b.StopTimer()
+			values := make([]Value, 10)
+			for i := 0; i < 10; i++ {
+				values[i] = NewValue(int64(i+1), float64(i))
+			}
+
+			otherValues := make([]Value, 10)
+			for i := 0; i < 10; i++ {
+				otherValues[i] = NewValue(1, float64(i))
+			}
+
+			entry, err := newEntryValues(values)
+			if err != nil {
+				b.Fatal(err)
+			}
+
+			b.StartTimer()
+			if err := entry.add(otherValues); err != nil {
+				b.Fatal(err)
+			}
+		}
+	})
+}