diff --git a/server/src/main/java/org/elasticsearch/index/mapper/CompletionFieldMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/CompletionFieldMapper.java
index af50dfbcb4e18..cf08d93a197de 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/CompletionFieldMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/CompletionFieldMapper.java
@@ -449,6 +449,10 @@ public Mapper parse(ParseContext context) throws IOException {
         // index
         for (Map.Entry<String, CompletionInputMetaData> completionInput : inputMap.entrySet()) {
             String input = completionInput.getKey();
+            if (input.trim().isEmpty()) {
+                context.addIgnoredField(fieldType.name());
+                continue;
+            }
             // truncate input
             if (input.length() > maxInputLength) {
                 int len = Math.min(maxInputLength, input.length());
diff --git a/server/src/test/java/org/elasticsearch/index/mapper/CompletionFieldMapperTests.java b/server/src/test/java/org/elasticsearch/index/mapper/CompletionFieldMapperTests.java
index be03a28a0aad2..1381b6e920559 100644
--- a/server/src/test/java/org/elasticsearch/index/mapper/CompletionFieldMapperTests.java
+++ b/server/src/test/java/org/elasticsearch/index/mapper/CompletionFieldMapperTests.java
@@ -397,6 +397,19 @@ public void testFieldValueValidation() throws Exception {
             assertThat(cause, instanceOf(IllegalArgumentException.class));
             assertThat(cause.getMessage(), containsString("[0x1e]"));
         }
+
+        // empty inputs are ignored
+        ParsedDocument doc = defaultMapper.parse(SourceToParse.source("test", "type1", "1", BytesReference
+                .bytes(XContentFactory.jsonBuilder()
+                    .startObject()
+                    .array("completion", "   ", "")
+                    .endObject()),
+            XContentType.JSON));
+        assertThat(doc.docs().size(), equalTo(1));
+        assertNull(doc.docs().get(0).get("completion"));
+        assertNotNull(doc.docs().get(0).getField("_ignored"));
+        IndexableField ignoredFields = doc.docs().get(0).getField("_ignored");
+        assertThat(ignoredFields.stringValue(), equalTo("completion"));
     }
 
     public void testPrefixQueryType() throws Exception {