diff --git a/README.txt b/README.txt
index 1fcbcf0..64027bb 100644
--- a/README.txt
+++ b/README.txt
@@ -3,7 +3,7 @@ Build requirements
 
 - JDK
 - Apache Ant
-- OpenSlide
+- OpenSlide >= 3.4.0
 
 Building on Linux or Mac OS X
 -----------------------------
diff --git a/openslide-jni.c b/openslide-jni.c
index bd5f8bc..26570b9 100644
--- a/openslide-jni.c
+++ b/openslide-jni.c
@@ -24,17 +24,20 @@
 #include <openslide.h>
 
 
-static jboolean osj_can_open(JNIEnv *env, jobject obj, jstring filename) {
+static jstring osj_detect_vendor(JNIEnv *env, jobject obj, jstring filename) {
   const char *filename2 = (*env)->GetStringUTFChars(env, filename, NULL);
   if (filename2 == NULL) {
-    return JNI_FALSE;
+    return NULL;
   }
 
-  jboolean result = openslide_can_open(filename2);
+  const char *val = openslide_detect_vendor(filename2);
 
   (*env)->ReleaseStringUTFChars(env, filename, filename2);
 
-  return result;
+  if (val == NULL) {
+    return NULL;
+  }
+  return (*env)->NewStringUTF(env, val);
 }
 
 static jlong osj_open(JNIEnv *env, jobject obj, jstring filename) {
@@ -190,7 +193,7 @@ static jstring osj_get_version(JNIEnv *env, jobject obj) {
 }
 
 static JNINativeMethod methods[] = {
-  { "openslide_can_open", "(Ljava/lang/String;)Z", (void *) osj_can_open },
+  { "openslide_detect_vendor", "(Ljava/lang/String;)Ljava/lang/String;", (void *) osj_detect_vendor },
   { "openslide_open", "(Ljava/lang/String;)J", (void *) osj_open },
   { "openslide_get_level_count", "(J)I", (void *) osj_get_level_count },
   { "openslide_get_level_dimensions", "(JI[J)V", (void *) osj_get_level_dimensions },
diff --git a/src/org/openslide/OpenSlide.java b/src/org/openslide/OpenSlide.java
index 8d7fb46..f3dfb3d 100644
--- a/src/org/openslide/OpenSlide.java
+++ b/src/org/openslide/OpenSlide.java
@@ -40,7 +40,7 @@
     private static final FileFilter FILE_FILTER = new FileFilter() {
         @Override
         public boolean accept(File f) {
-            return f.isDirectory() || OpenSlide.fileIsValid(f);
+            return f.isDirectory() || OpenSlide.detectVendor(f) != null;
         }
 
         @Override
@@ -84,8 +84,8 @@ public String getDescription() {
 
     final private int hashCodeVal;
 
-    public static boolean fileIsValid(File file) {
-        return OpenSlideJNI.openslide_can_open(file.getPath());
+    public static String detectVendor(File file) {
+        return OpenSlideJNI.openslide_detect_vendor(file.getPath());
     }
 
     public OpenSlide(File file) throws IOException {
diff --git a/src/org/openslide/OpenSlideJNI.java b/src/org/openslide/OpenSlideJNI.java
index 2e652a8..32c14d4 100644
--- a/src/org/openslide/OpenSlideJNI.java
+++ b/src/org/openslide/OpenSlideJNI.java
@@ -56,7 +56,7 @@ private OpenSlideJNI() {
         }
     }
 
-    native static boolean openslide_can_open(String file);
+    native static String openslide_detect_vendor(String file);
 
     native static long openslide_open(String file);
 
diff --git a/src/org/openslide/TestCLI.java b/src/org/openslide/TestCLI.java
index 53213d1..10dde39 100644
--- a/src/org/openslide/TestCLI.java
+++ b/src/org/openslide/TestCLI.java
@@ -48,8 +48,8 @@ public static void main(String args[]) throws IOException {
 
         File f = new File(args[0]);
 
-        System.out.printf("openslide_can_open returns %s\n", OpenSlide
-                .fileIsValid(f) ? "true" : "false");
+        System.out.printf("openslide_detect_vendor returns %s\n",
+                OpenSlide.detectVendor(f));
         OpenSlide osr = new OpenSlide(f);
 
         long w, h;