diff --git a/db.go b/db.go
index 6ef35ea..35a56e8 100644
--- a/db.go
+++ b/db.go
@@ -212,7 +212,7 @@ func (db *DB) munmap() error {
 // mmapSize determines the appropriate size for the mmap given the current size
 // of the database. The minimum size is 4MB and doubles until it reaches 1GB.
 func (db *DB) mmapSize(size int) int {
-	if size < minMmapSize {
+	if size <= minMmapSize {
 		return minMmapSize
 	} else if size < maxMmapStep {
 		size *= 2
diff --git a/db_test.go b/db_test.go
index e689836..0b4e840 100644
--- a/db_test.go
+++ b/db_test.go
@@ -297,7 +297,8 @@ func TestDB_mmapSize(t *testing.T) {
 	assert.Equal(t, db.mmapSize(0), minMmapSize)
 	assert.Equal(t, db.mmapSize(16384), minMmapSize)
 	assert.Equal(t, db.mmapSize(minMmapSize-1), minMmapSize)
-	assert.Equal(t, db.mmapSize(minMmapSize), minMmapSize*2)
+	assert.Equal(t, db.mmapSize(minMmapSize), minMmapSize)
+	assert.Equal(t, db.mmapSize(minMmapSize+1), (minMmapSize*2)+4096)
 	assert.Equal(t, db.mmapSize(10000000), 20000768)
 	assert.Equal(t, db.mmapSize((1<<30)-1), 2147483648)
 	assert.Equal(t, db.mmapSize(1<<30), 1<<31)