diff --git a/olca-core/src/main/java/org/openlca/core/matrix/io/npy/DenseReader.java b/olca-core/src/main/java/org/openlca/core/matrix/io/npy/DenseReader.java
index ac68f1c5d..772c4d7c6 100644
--- a/olca-core/src/main/java/org/openlca/core/matrix/io/npy/DenseReader.java
+++ b/olca-core/src/main/java/org/openlca/core/matrix/io/npy/DenseReader.java
@@ -42,6 +42,12 @@ DenseMatrix run() {
 					}
 				}
 			}
+			buf.force();
+
+			// there is no way to close the buffer here
+			// see: https://github.com/GreenDelta/olca-modules/issues/17
+			// System.gc();
+
 			return matrix;
 		} catch (IOException e) {
 			throw new RuntimeException("failed to read from " + file, e);
diff --git a/olca-core/src/test/java/org/openlca/core/matrix/io/npy/HeaderTest.java b/olca-core/src/test/java/org/openlca/core/matrix/io/npy/HeaderTest.java
index 432a75889..0be45a66b 100644
--- a/olca-core/src/test/java/org/openlca/core/matrix/io/npy/HeaderTest.java
+++ b/olca-core/src/test/java/org/openlca/core/matrix/io/npy/HeaderTest.java
@@ -3,12 +3,8 @@
 import org.junit.Assert;
 import org.junit.Test;
 import org.openlca.core.matrix.format.DenseMatrix;
-import sun.misc.Cleaner;
 
 import java.io.File;
-import java.io.RandomAccessFile;
-import java.nio.MappedByteBuffer;
-import java.nio.channels.FileChannel;
 import java.nio.file.Files;
 
 public class HeaderTest {
@@ -35,26 +31,10 @@ public void testFromReadFile() throws Exception {
 		Assert.assertEquals("<f8", h.dtype);
 		Assert.assertTrue(h.fortranOrder);
 		Assert.assertArrayEquals(new int[]{2, 3}, h.shape);
-		Assert.assertTrue(file.delete());
-	}
-
-	@Test
-	public void testDeleteTempFile() throws Exception {
-		File file = Files.createTempFile("_file_del_test", ".txt").toFile();
-		try (RandomAccessFile f = new RandomAccessFile(file, "rw");
-		     FileChannel chan = f.getChannel()) {
-			MappedByteBuffer buf = chan.map(
-					FileChannel.MapMode.READ_WRITE, 0, 42);
-			for (int i = 0; i < 42; i++) {
-				buf.put((byte) 42);
-			}
-			buf.force();
-			Cleaner cleaner = ((sun.nio.ch.DirectBuffer) buf).cleaner();
-			if (cleaner != null) {
-				cleaner.clean();
-			}
+		if (!file.delete()) {
+			// deleting the file will probably fail on Windows
+			// see https://github.com/GreenDelta/olca-modules/issues/17
+			file.deleteOnExit();
 		}
-		Assert.assertTrue(file.delete());
 	}
-
 }