diff --git a/MaxMind.Db.Test/ThreadingTest.cs b/MaxMind.Db.Test/ThreadingTest.cs
index d72d121..66ddd32 100644
--- a/MaxMind.Db.Test/ThreadingTest.cs
+++ b/MaxMind.Db.Test/ThreadingTest.cs
@@ -12,9 +12,11 @@ namespace MaxMind.Db.Test
     public class ThreadingTest
     {
         [Test]
-        public void TestParallelFor()
+        [TestCase(FileAccessMode.MemoryMapped)]
+        [TestCase(FileAccessMode.Memory)]
+        public void TestParallelFor(FileAccessMode mode)
         {
-            var reader = new Reader(Path.Combine("..", "..", "TestData", "GeoLite2-City.mmdb"), FileAccessMode.MemoryMapped);
+            var reader = new Reader(Path.Combine("..", "..", "TestData", "GeoLite2-City.mmdb"), mode);
             var count = 0;
             var ipsAndResults = new Dictionary<IPAddress, string>();
             var rand = new Random();
@@ -45,12 +47,14 @@ public void TestParallelFor()
         }
 
         [Test]
+        [TestCase(FileAccessMode.MemoryMapped)]
+        [TestCase(FileAccessMode.Memory)]
         [Category("BreaksMono")]
-        public void TestManyOpens()
+        public void TestManyOpens(FileAccessMode mode)
         {
             Parallel.For(0, 1000, i =>
             {
-                var reader = new Reader(Path.Combine("..", "..", "TestData", "GeoLite2-City.mmdb"), FileAccessMode.MemoryMapped);
+                var reader = new Reader(Path.Combine("..", "..", "TestData", "GeoLite2-City.mmdb"), mode);
             });
         }
     }
diff --git a/MaxMind.Db/Reader.cs b/MaxMind.Db/Reader.cs
index 7a64394..b286a25 100644
--- a/MaxMind.Db/Reader.cs
+++ b/MaxMind.Db/Reader.cs
@@ -65,7 +65,7 @@ private int IPV4Start
             }
         }
 
-        private static readonly Object _mmapLocker = new Object();
+        private static readonly Object _fileLocker = new Object();
 
         private readonly ThreadLocal<Stream> _stream;
 
@@ -90,7 +90,7 @@ public Reader(string file, FileAccessMode mode)
             {
                 var fileInfo = new FileInfo(file);
                 var mmfName = fileInfo.FullName.Replace("\\", "-");
-                lock (_mmapLocker)
+                lock (_fileLocker)
                 {
                     try
                     {
@@ -109,18 +109,23 @@ public Reader(string file, FileAccessMode mode)
                 }
             }
 
-            _stream = new ThreadLocal<Stream>(() =>
+            if (mode == FileAccessMode.Memory)
             {
-                Stream s;
-                if (mode == FileAccessMode.Memory) s = new MemoryStream(File.ReadAllBytes(_fileName));
-                else
+                byte[] fileBytes = File.ReadAllBytes(_fileName);
+                _stream = new ThreadLocal<Stream>(() =>
+                {
+                    return new MemoryStream(fileBytes, false);
+                });
+            }
+            else
+            {
+                _stream = new ThreadLocal<Stream>(() =>
                 {
-                    var fileLength = (int)new FileInfo(file).Length;
-                    s = _memoryMappedFile.CreateViewStream(0, fileLength, MemoryMappedFileAccess.Read);
-                }
 
-                return s;
-            });
+                    var fileLength = (int)new FileInfo(file).Length;
+                    return _memoryMappedFile.CreateViewStream(0, fileLength, MemoryMappedFileAccess.Read);
+                });
+            }
 
             var start = FindMetadataStart();
             var metaDecode = new Decoder(_stream, start);