diff --git a/src/main/java/com/android/tools/r8/utils/ArchiveResourceProvider.java b/src/main/java/com/android/tools/r8/utils/ArchiveResourceProvider.java
index 37aa208..499ba47 100644
--- a/src/main/java/com/android/tools/r8/utils/ArchiveResourceProvider.java
+++ b/src/main/java/com/android/tools/r8/utils/ArchiveResourceProvider.java
@@ -54,17 +54,18 @@
       while (entries.hasMoreElements()) {
         ZipEntry entry = entries.nextElement();
         try (InputStream stream = zipFile.getInputStream(entry)) {
-          Path name = Paths.get(entry.getName());
-          Origin entryOrigin = new ArchiveEntryOrigin(entry.getName(), origin);
-          if (archive.matchesFile(name)) {
-            if (isDexFile(name)) {
+          String name = entry.getName();
+          Path path = Paths.get(name);
+          Origin entryOrigin = new ArchiveEntryOrigin(name, origin);
+          if (archive.matchesFile(path)) {
+            if (isDexFile(path)) {
               if (!ignoreDexInArchive) {
                 ProgramResource resource =
                     OneShotByteResource.create(
                         Kind.DEX, entryOrigin, ByteStreams.toByteArray(stream), null);
                 dexResources.add(resource);
               }
-            } else if (isClassFile(name)) {
+            } else if (isClassFile(path)) {
               String descriptor = DescriptorUtils.guessTypeDescriptor(name);
               ProgramResource resource =
                   OneShotByteResource.create(
diff --git a/src/main/java/com/android/tools/r8/utils/DescriptorUtils.java b/src/main/java/com/android/tools/r8/utils/DescriptorUtils.java
index fa045e6..a846ea7 100644
--- a/src/main/java/com/android/tools/r8/utils/DescriptorUtils.java
+++ b/src/main/java/com/android/tools/r8/utils/DescriptorUtils.java
@@ -341,22 +341,35 @@
     }
   }
 
-  // Guess class descriptor from location of the class file.
+  /**
+   * Guess class descriptor from location of the class file on the file system
+   *
+   * @param name Path of the file to convert to the corresponding descriptor
+   * @return java class descriptor
+   */
   public static String guessTypeDescriptor(Path name) {
-    return guessTypeDescriptor(name.toString());
+    String fileName = name.toString();
+    if (File.separatorChar != '/') {
+      fileName = fileName.replace(File.separatorChar, '/');
+    }
+    return guessTypeDescriptor(fileName);
   }
 
-  // Guess class descriptor from location of the class file.
+  /**
+   * Guess class descriptor from location of the class file. This method assumes that the
+   * name uses '/' as the separator. Therefore, this should not be the name of a file
+   * on a file system.
+   *
+   * @param name the location of the class file to convert to descriptor
+   * @return java class descriptor
+   */
   public static String guessTypeDescriptor(String name) {
     assert name != null;
     assert name.endsWith(CLASS_EXTENSION) :
         "Name " + name + " must have " + CLASS_EXTENSION + " suffix";
-    String fileName =
-        File.separatorChar == '/' ? name.toString() :
-            name.toString().replace(File.separatorChar, '/');
-    String descriptor = fileName.substring(0, fileName.length() - CLASS_EXTENSION.length());
+    String descriptor = name.substring(0, name.length() - CLASS_EXTENSION.length());
     if (descriptor.contains(".")) {
-      throw new CompilationError("Unexpected class file name: " + fileName);
+      throw new CompilationError("Unexpected class file name: " + name);
     }
     return 'L' + descriptor + ';';
   }
diff --git a/src/test/java/com/android/tools/r8/utils/DescriptorUtilsTest.java b/src/test/java/com/android/tools/r8/utils/DescriptorUtilsTest.java
index 58180e3..7ad9163 100644
--- a/src/test/java/com/android/tools/r8/utils/DescriptorUtilsTest.java
+++ b/src/test/java/com/android/tools/r8/utils/DescriptorUtilsTest.java
@@ -6,7 +6,10 @@
 
 import static org.junit.Assert.assertEquals;
 
+import java.io.File;
 import java.io.IOException;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 import org.junit.Test;
 
 public class DescriptorUtilsTest {
@@ -67,4 +70,16 @@
     assertEquals("java.lang.Object", DescriptorUtils.descriptorToJavaType("Ljava/lang/Object;"));
     assertEquals("a.b.C", DescriptorUtils.descriptorToJavaType("La/b/C;"));
   }
+
+  @Test
+  public void guessClassDescriptor() {
+    String obj = "java/lang/Object.class";
+    assertEquals("Ljava/lang/Object;", DescriptorUtils.guessTypeDescriptor(obj));
+    String objBackslash = "java\\lang\\Object.class";
+    assertEquals("Ljava\\lang\\Object;", DescriptorUtils.guessTypeDescriptor(objBackslash));
+    String objFileSeparatorChar =
+        "java" + File.separatorChar + "lang" + File.separatorChar + "Object.class";
+    assertEquals("Ljava/lang/Object;",
+        DescriptorUtils.guessTypeDescriptor(Paths.get(objFileSeparatorChar)));
+  }
 }