Index: lucene/src/test/org/apache/lucene/util/automaton/AutomatonTestUtil.java
===================================================================
--- lucene/src/test/org/apache/lucene/util/automaton/AutomatonTestUtil.java	(revision 979453)
+++ lucene/src/test/org/apache/lucene/util/automaton/AutomatonTestUtil.java	(working copy)
@@ -77,12 +77,44 @@
     return new String(buffer, 0, end);
   }
   
-  // picks a random int code point that this transition
-  // accepts, avoiding the surrogates range since they are
-  // "defined" in UTF32.  Don't call this on a transition
-  // that only accepts UTF16 surrogate values!!
+  // picks a random int code point, avoiding surrogates;
+  // throws IllegalArgumentException if this transition only
+  // accepts surrogates
   private static int getRandomCodePoint(final Random r, final Transition t) {
-    return t.min+r.nextInt(t.max-t.min+1);
+    final int code;
+    if (t.max < UnicodeUtil.UNI_SUR_HIGH_START ||
+        t.min > UnicodeUtil.UNI_SUR_HIGH_END) {
+      // easy: entire range is before or after surrogates
+      code = t.min+r.nextInt(t.max-t.min+1);
+    } else if (t.min >= UnicodeUtil.UNI_SUR_HIGH_START) {
+      if (t.max > UnicodeUtil.UNI_SUR_LOW_END) {
+        // after surrogates
+        code = 1+UnicodeUtil.UNI_SUR_LOW_END+r.nextInt(t.max-UnicodeUtil.UNI_SUR_LOW_END+1);
+      } else {
+        throw new IllegalArgumentException("transition accepts only surrogates: " + t);
+      }
+    } else if (t.max <= UnicodeUtil.UNI_SUR_LOW_END) {
+      if (t.min < UnicodeUtil.UNI_SUR_HIGH_START) {
+        // before surrogates
+        code = t.min + r.nextInt(UnicodeUtil.UNI_SUR_HIGH_START - t.min);
+      } else {
+        throw new IllegalArgumentException("transition accepts only surrogates: " + t);
+      }
+    } else {
+      // range includes all surrogates
+      int gap1 = UnicodeUtil.UNI_SUR_HIGH_START - t.min;
+      int gap2 = t.max - UnicodeUtil.UNI_SUR_LOW_END;
+      int c = r.nextInt(gap1+gap2);
+      if (c < gap1) {
+        code = t.min + c;
+      } else {
+        code = UnicodeUtil.UNI_SUR_LOW_END + c - gap1 + 1;
+      }
+    }
+
+    assert code >= t.min && code <= t.max && (code < UnicodeUtil.UNI_SUR_HIGH_START || code > UnicodeUtil.UNI_SUR_LOW_END):
+      "code=" + code + " min=" + t.min + " max=" + t.max;
+    return code;
   }
 
   public static class RandomAcceptedStrings {
@@ -206,7 +238,6 @@
           } else {
             t = s.transitionsArray[r.nextInt(s.numTransitions)];
           }
-          
           soFar.add(getRandomCodePoint(r, t));
           s = t.to;
         }
Index: lucene/src/test/org/apache/lucene/util/automaton/TestBasicOperations.java
===================================================================
--- lucene/src/test/org/apache/lucene/util/automaton/TestBasicOperations.java	(revision 979453)
+++ lucene/src/test/org/apache/lucene/util/automaton/TestBasicOperations.java	(working copy)
@@ -100,6 +100,9 @@
         int[] acc = null;
         try {
           acc = rx.getRandomAcceptedString(r);
+          if (acc == null) {
+            continue;
+          }
           final String s = UnicodeUtil.newString(acc, 0, acc.length);
           assertTrue(BasicOperations.run(a, s));
         } catch (Throwable t) {
Index: lucene/src/test/org/apache/lucene/util/automaton/TestUTF32ToUTF8.java
===================================================================
--- lucene/src/test/org/apache/lucene/util/automaton/TestUTF32ToUTF8.java	(revision 979453)
+++ lucene/src/test/org/apache/lucene/util/automaton/TestUTF32ToUTF8.java	(working copy)
@@ -222,6 +222,9 @@
       } else {
         // will be accepted
         int[] codepoints = ras.getRandomAcceptedString(random);
+        if (codepoints == null) {
+          continue;
+        }
         try {
           string = UnicodeUtil.newString(codepoints, 0, codepoints.length);
         } catch (Exception e) {
Index: lucene/src/java/org/apache/lucene/util/UnicodeUtil.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/UnicodeUtil.java	(revision 979453)
+++ lucene/src/java/org/apache/lucene/util/UnicodeUtil.java	(working copy)
@@ -701,4 +701,12 @@
     }
     return sb.toString();
   }
+
+  public static boolean isHighSurrogate(int code) {
+    return code >= UNI_SUR_HIGH_START && code <= UNI_SUR_HIGH_END;
+  }
+
+  public static boolean isLowSurrogate(int code) {
+    return code >= UNI_SUR_LOW_START && code <= UNI_SUR_LOW_END;
+  }
 }