diff --git a/src/main/java/org/elasticsearch/index/mapper/core/CompletionFieldMapper.java b/src/main/java/org/elasticsearch/index/mapper/core/CompletionFieldMapper.java
index e4e4a36ae18..ce7e4bf40a7 100644
--- a/src/main/java/org/elasticsearch/index/mapper/core/CompletionFieldMapper.java
+++ b/src/main/java/org/elasticsearch/index/mapper/core/CompletionFieldMapper.java
@@ -40,6 +40,7 @@ import org.elasticsearch.search.suggest.completion.CompletionTokenStream;
 import java.io.IOException;
 import java.io.Reader;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 /**
@@ -276,10 +277,18 @@ public class CompletionFieldMapper extends AbstractFieldMapper<String> {
     }
 
     public Field getCompletionField(String input, BytesRef payload) {
+        final String originalInput = input;
         if (input.length() > maxInputLength) {
             final int len = correctSubStringLen(input, Math.min(maxInputLength, input.length()));
             input = input.substring(0, len);    
         }
+        for (int i = 0; i < input.length(); i++) {
+            if (isReservedChar(input.charAt(i))) {
+                throw new ElasticSearchIllegalArgumentException("Illegal input [" + originalInput + "] UTF-16 codepoint  [0x"
+                        + Integer.toHexString((int) input.charAt(i)).toUpperCase(Locale.ROOT)                        
+                        + "] at position " + i + " is a reserved character");
+            }
+        }
         return new SuggestField(names().fullName(), input, this.fieldType, payload, analyzingSuggestLookupProvider);
     }
     
@@ -388,4 +397,14 @@ public class CompletionFieldMapper extends AbstractFieldMapper<String> {
             this.maxInputLength = fieldMergeWith.maxInputLength;
         }
     }
+    
+    private static final char END_LABEL = 0x00;
+    
+    // this should be package private but our tests don't allow it.
+    public static boolean isReservedChar(char character) {
+        /* we also use 0xFF as a SEP_LABEL in the suggester but it's not valid UTF-8 so no need to check.
+         *  we also don't need to convert to UTF-8 here to check for the 0x00 end label since all multi-byte
+         *  UTF-8 chars start with 0x10 binary so if the UTF-16 CP is == 0x00 it's the single byte UTF-8 CP */
+        return character == END_LABEL;
+    }
 }
diff --git a/src/test/java/org/elasticsearch/test/integration/search/suggest/CompletionSuggestSearchTests.java b/src/test/java/org/elasticsearch/test/integration/search/suggest/CompletionSuggestSearchTests.java
index 4d21134f146..3a5d0e301bd 100644
--- a/src/test/java/org/elasticsearch/test/integration/search/suggest/CompletionSuggestSearchTests.java
+++ b/src/test/java/org/elasticsearch/test/integration/search/suggest/CompletionSuggestSearchTests.java
@@ -32,6 +32,7 @@ import org.elasticsearch.common.settings.ImmutableSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.index.mapper.MapperException;
+import org.elasticsearch.index.mapper.MapperParsingException;
 import org.elasticsearch.index.mapper.core.CompletionFieldMapper;
 import org.elasticsearch.search.suggest.Suggest;
 import org.elasticsearch.search.suggest.completion.CompletionStats;
@@ -726,7 +727,7 @@ public class CompletionSuggestSearchTests extends AbstractSharedClusterTest {
         int iters = atLeast(10);
         for (int i = 0; i < iters; i++) {
             int len = between(3, 50);
-            String str = randomRealisticUnicodeOfCodepointLengthBetween(len+1, atLeast(len + 2));
+            String str = replaceReservedChars(randomRealisticUnicodeOfCodepointLengthBetween(len+1, atLeast(len + 2)), (char)0x01);
             ElasticsearchAssertions.assertAcked(client().admin().indices().preparePutMapping(INDEX).setType(TYPE).setSource(jsonBuilder().startObject()
                     .startObject(TYPE).startObject("properties")
                     .startObject(FIELD)
@@ -766,7 +767,7 @@ public class CompletionSuggestSearchTests extends AbstractSharedClusterTest {
                 .endObject()));
         ensureYellow();
         // can cause stack overflow without the default max_input_len
-        String longString = randomRealisticUnicodeOfLength(atLeast(5000));
+        String longString = replaceReservedChars(randomRealisticUnicodeOfLength(atLeast(5000)), (char)0x01);
         client().prepareIndex(INDEX, TYPE, "1").setSource(jsonBuilder()
                 .startObject().startObject(FIELD)
                 .startArray("input").value(longString).endArray()
@@ -775,4 +776,37 @@ public class CompletionSuggestSearchTests extends AbstractSharedClusterTest {
         ).setRefresh(true).get();
         
     }
+    
+    // see #3648
+    @Test(expected = MapperParsingException.class)
+    public void testReservedChars()  throws IOException {
+        client().admin().indices().prepareCreate(INDEX).get();
+        ElasticsearchAssertions.assertAcked(client().admin().indices().preparePutMapping(INDEX).setType(TYPE).setSource(jsonBuilder().startObject()
+                .startObject(TYPE).startObject("properties")
+                .startObject(FIELD)
+                .field("type", "completion")
+                .endObject()
+                .endObject().endObject()
+                .endObject()));
+        ensureYellow();
+        // can cause stack overflow without the default max_input_len
+        String string = "foo" + (char)0x00 +  "bar";
+        client().prepareIndex(INDEX, TYPE, "1").setSource(jsonBuilder()
+                .startObject().startObject(FIELD)
+                .startArray("input").value(string).endArray()
+                .field("output", "foobar")
+                .endObject().endObject()
+        ).setRefresh(true).get();
+        
+    }
+    
+    private static String replaceReservedChars(String input, char replacement) {
+        char[] charArray = input.toCharArray();
+        for (int i = 0; i < charArray.length; i++) {
+            if (CompletionFieldMapper.isReservedChar(charArray[i])) {
+                charArray[i] = replacement;
+            }
+        }
+        return new String(charArray);
+    }
 }