diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index a137ef2b67a..2d8d20e329e 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -79,6 +79,10 @@ Bug Fixes
   Also, ensure immutability and use only one instance of this table in RAM (lazy
   loaded) since its quite large. (sausarkar, Steven Rowe, Robert Muir)
 
+* LUCENE-4310: MappingCharFilter was failing to match input strings
+  containing non-BMP Unicode characters.  (Dawid Weiss, Robert Muir,
+  Mike McCandless)
+
 Build
 
 * LUCENE-3985: Upgrade to randomizedtesting 2.0.0. Added support for 
diff --git a/lucene/analysis/common/src/java/org/apache/lucene/analysis/charfilter/NormalizeCharMap.java b/lucene/analysis/common/src/java/org/apache/lucene/analysis/charfilter/NormalizeCharMap.java
index c6470611d2c..c22203a76a4 100644
--- a/lucene/analysis/common/src/java/org/apache/lucene/analysis/charfilter/NormalizeCharMap.java
+++ b/lucene/analysis/common/src/java/org/apache/lucene/analysis/charfilter/NormalizeCharMap.java
@@ -111,9 +111,8 @@ public class NormalizeCharMap {
         final org.apache.lucene.util.fst.Builder<CharsRef> builder = new org.apache.lucene.util.fst.Builder<CharsRef>(FST.INPUT_TYPE.BYTE2, outputs);
         final IntsRef scratch = new IntsRef();
         for(Map.Entry<String,String> ent : pendingPairs.entrySet()) {
-          builder.add(Util.toUTF32(ent.getKey(), scratch),
+          builder.add(Util.toUTF16(ent.getKey(), scratch),
                       new CharsRef(ent.getValue()));
-      
         }
         map = builder.finish();
         pendingPairs.clear();
diff --git a/lucene/analysis/common/src/test/org/apache/lucene/analysis/charfilter/TestMappingCharFilter.java b/lucene/analysis/common/src/test/org/apache/lucene/analysis/charfilter/TestMappingCharFilter.java
index c4fab5519c0..d692a57c328 100644
--- a/lucene/analysis/common/src/test/org/apache/lucene/analysis/charfilter/TestMappingCharFilter.java
+++ b/lucene/analysis/common/src/test/org/apache/lucene/analysis/charfilter/TestMappingCharFilter.java
@@ -33,6 +33,7 @@ import org.apache.lucene.analysis.CharFilter;
 import org.apache.lucene.analysis.MockTokenizer;
 import org.apache.lucene.analysis.TokenStream;
 import org.apache.lucene.analysis.Tokenizer;
+import org.apache.lucene.util.UnicodeUtil;
 import org.apache.lucene.util._TestUtil;
 
 public class TestMappingCharFilter extends BaseTokenStreamTestCase {
@@ -55,6 +56,11 @@ public class TestMappingCharFilter extends BaseTokenStreamTestCase {
 
     builder.add( "empty", "" );
 
+    // BMP (surrogate pair):
+    builder.add(UnicodeUtil.newString(new int[] {0x1D122}, 0, 1), "fclef");
+
+    builder.add("\uff01", "full width exclamation");
+
     normMap = builder.build();
   }
 
@@ -128,6 +134,18 @@ public class TestMappingCharFilter extends BaseTokenStreamTestCase {
     assertTokenStreamContents(ts, new String[0], new int[]{}, new int[]{}, 5);
   }
 
+  public void testNonBMPChar() throws Exception {
+    CharFilter cs = new MappingCharFilter( normMap, new StringReader( UnicodeUtil.newString(new int[] {0x1D122}, 0, 1) ) );
+    TokenStream ts = new MockTokenizer(cs, MockTokenizer.WHITESPACE, false);
+    assertTokenStreamContents(ts, new String[]{"fclef"}, new int[]{0}, new int[]{2}, 2);
+  }
+
+  public void testFullWidthChar() throws Exception {
+    CharFilter cs = new MappingCharFilter( normMap, new StringReader( "\uff01") );
+    TokenStream ts = new MockTokenizer(cs, MockTokenizer.WHITESPACE, false);
+    assertTokenStreamContents(ts, new String[]{"full width exclamation"}, new int[]{0}, new int[]{1}, 1);
+  }
+
   //
   //                1111111111222
   //      01234567890123456789012
diff --git a/lucene/core/src/java/org/apache/lucene/util/fst/Util.java b/lucene/core/src/java/org/apache/lucene/util/fst/Util.java
index 55823a3f829..7a9685745ed 100644
--- a/lucene/core/src/java/org/apache/lucene/util/fst/Util.java
+++ b/lucene/core/src/java/org/apache/lucene/util/fst/Util.java
@@ -767,6 +767,21 @@ public final class Util {
     }
   }
 
+  /** Just maps each UTF16 unit (char) to the ints in an
+   *  IntsRef. */
+  public static IntsRef toUTF16(CharSequence s, IntsRef scratch) {
+    final int charLimit = s.length();
+    scratch.grow(charLimit);
+    int idx = 0;
+    while(idx < charLimit) {
+      scratch.ints[idx] = (int) s.charAt(idx);
+      idx++;
+    }
+    scratch.offset = 0;
+    scratch.length = idx;
+    return scratch;
+  }
+
   /** Decodes the Unicode codepoints from the provided
    *  CharSequence and places them in the provided scratch
    *  IntsRef, which must not be null, returning it. */