diff --git a/luni/src/main/native/libcore_icu_NativeIDN.cpp b/luni/src/main/native/libcore_icu_NativeIDN.cpp
index 43f3ce5..9786b9d 100644
--- a/luni/src/main/native/libcore_icu_NativeIDN.cpp
+++ b/luni/src/main/native/libcore_icu_NativeIDN.cpp
@@ -37,7 +37,8 @@
     if (src.get() == NULL) {
         return NULL;
     }
-    UChar dst[256];
+    static const size_t kDstSize = 512;
+    UChar dst[kDstSize];
     UErrorCode status = U_ZERO_ERROR;
 
     // We're stuck implementing IDNA-2003 for now since that's what we specify.
@@ -47,10 +48,10 @@
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
     size_t resultLength = toAscii
-        ? uidna_IDNToASCII(src.get(), src.size(), &dst[0], sizeof(dst), flags, NULL, &status)
-        : uidna_IDNToUnicode(src.get(), src.size(), &dst[0], sizeof(dst), flags, NULL, &status);
+        ? uidna_IDNToASCII(src.get(), src.size(), &dst[0], kDstSize, flags, NULL, &status)
+        : uidna_IDNToUnicode(src.get(), src.size(), &dst[0], kDstSize, flags, NULL, &status);
 #pragma GCC diagnostic pop
-
+    
     if (U_FAILURE(status)) {
         jniThrowException(env, "java/lang/IllegalArgumentException", u_errorName(status));
         return NULL;
diff --git a/luni/src/test/java/libcore/java/net/IDNTest.java b/luni/src/test/java/libcore/java/net/IDNTest.java
index f01eca3..37f3505 100644
--- a/luni/src/test/java/libcore/java/net/IDNTest.java
+++ b/luni/src/test/java/libcore/java/net/IDNTest.java
@@ -37,4 +37,15 @@
         String longInput = makePunyString(512);
         assertEquals(longInput, IDN.toUnicode(longInput));
     }
+
+    // http://b/30765246
+    public void testLongDomainName() {
+        String label63 = "123456789-123456789-123456789-123456789-123456789-123456789-123";
+        String host255 = label63 + "." + label63 + "." + label63 + "." + label63;
+        try {
+            IDN.toASCII(host255.substring(3) + ".com");
+            fail();
+        } catch (IllegalArgumentException expected) {
+        }
+    }
 }