diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 5c7e12fc579..d02ed269f72 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -248,6 +248,11 @@ Bug Fixes
 * LUCENE-6872: IndexWriter handles any VirtualMachineError, not just OOM,
   as tragic. (Robert Muir)
 
+* LUCENE-6814: PatternTokenizer no longer hangs onto heap sized to the
+  maximum input string it's ever seen, which can be a large memory
+  "leak" if you tokenize large strings with many threads across many
+  indices (Alex Chow via Mike McCandless)
+
 Other
 
 * LUCENE-6478: Test execution can hang with java.security.debug. (Dawid Weiss)
diff --git a/lucene/analysis/common/src/java/org/apache/lucene/analysis/pattern/PatternTokenizer.java b/lucene/analysis/common/src/java/org/apache/lucene/analysis/pattern/PatternTokenizer.java
index faa7e91d63a..e25a7b9f1a1 100644
--- a/lucene/analysis/common/src/java/org/apache/lucene/analysis/pattern/PatternTokenizer.java
+++ b/lucene/analysis/common/src/java/org/apache/lucene/analysis/pattern/PatternTokenizer.java
@@ -136,10 +136,20 @@ public final class PatternTokenizer extends Tokenizer {
     offsetAtt.setOffset(ofs, ofs);
   }
 
+  @Override
+  public void close() throws IOException {
+    try {
+      super.close();
+    } finally {
+      str.setLength(0);
+      str.trimToSize();
+    }
+  }
+
   @Override
   public void reset() throws IOException {
     super.reset();
-    fillBuffer(str, input);
+    fillBuffer(input);
     matcher.reset(str);
     index = 0;
   }
@@ -147,11 +157,11 @@ public final class PatternTokenizer extends Tokenizer {
   // TODO: we should see if we can make this tokenizer work without reading
   // the entire document into RAM, perhaps with Matcher.hitEnd/requireEnd ?
   final char[] buffer = new char[8192];
-  private void fillBuffer(StringBuilder sb, Reader input) throws IOException {
+  private void fillBuffer(Reader input) throws IOException {
     int len;
-    sb.setLength(0);
+    str.setLength(0);
     while ((len = input.read(buffer)) > 0) {
-      sb.append(buffer, 0, len);
+      str.append(buffer, 0, len);
     }
   }
 }
diff --git a/lucene/analysis/common/src/test/org/apache/lucene/analysis/pattern/TestPatternTokenizer.java b/lucene/analysis/common/src/test/org/apache/lucene/analysis/pattern/TestPatternTokenizer.java
index 316fbdb5b6f..30badb8c14e 100644
--- a/lucene/analysis/common/src/test/org/apache/lucene/analysis/pattern/TestPatternTokenizer.java
+++ b/lucene/analysis/common/src/test/org/apache/lucene/analysis/pattern/TestPatternTokenizer.java
@@ -146,4 +146,37 @@ public class TestPatternTokenizer extends BaseTokenStreamTestCase
     checkRandomData(random(), b, 1000*RANDOM_MULTIPLIER);
     b.close();
   }
+
+  // LUCENE-6814
+  public void testHeapFreedAfterClose() throws Exception {
+    // TODO: can we move this to BaseTSTC to catch other "hangs onto heap"ers?
+
+    // Build a 1MB string:
+    StringBuilder b = new StringBuilder();
+    for(int i=0;i<1024;i++) {
+      // 1023 spaces, then an x
+      for(int j=0;j<1023;j++) {
+        b.append(' ');
+      }
+      b.append('x');
+    }
+
+    String big = b.toString();
+
+    Pattern x = Pattern.compile("x");
+
+    List<Tokenizer> tokenizers = new ArrayList<>();
+    for(int i=0;i<512;i++) {
+      Tokenizer stream = new PatternTokenizer(x, -1);
+      tokenizers.add(stream);
+      stream.setReader(new StringReader(big));
+      stream.reset();
+      for(int j=0;j<1024;j++) {
+        assertTrue(stream.incrementToken());
+      }
+      assertFalse(stream.incrementToken());
+      stream.end();
+      stream.close();
+    }
+  }
 }