diff --git a/guava-tests/test/com/google/common/io/BaseEncodingTest.java b/guava-tests/test/com/google/common/io/BaseEncodingTest.java
index 3780ede9361a..29e9f907944c 100644
--- a/guava-tests/test/com/google/common/io/BaseEncodingTest.java
+++ b/guava-tests/test/com/google/common/io/BaseEncodingTest.java
@@ -558,6 +558,17 @@ private static void testStreamingDecodes(BaseEncoding encoding, String encoded,
 }
 }
 
+ @GwtIncompatible // Writer
+ public void testEncodingStream_closeIsIdempotent() throws IOException {
+ StringWriter writer = new StringWriter();
+ OutputStream encodingStream = base64().encodingStream(writer);
+ encodingStream.write(0);
+ encodingStream.close();
+ assertThat(writer.toString()).isEqualTo("AA==");
+ encodingStream.close();
+ assertThat(writer.toString()).isEqualTo("AA==");
+ }
+
 public void testToString() {
 assertThat(base64().toString()).isEqualTo("BaseEncoding.base64().withPadChar('=')");
 assertThat(base32Hex().omitPadding().toString())
diff --git a/guava/src/com/google/common/io/BaseEncoding.java b/guava/src/com/google/common/io/BaseEncoding.java
index 44a2281ecf24..8b292d95bb01 100644
--- a/guava/src/com/google/common/io/BaseEncoding.java
+++ b/guava/src/com/google/common/io/BaseEncoding.java
@@ -646,6 +646,7 @@ public OutputStream encodingStream(Writer out) {
 int bitBuffer = 0;
 int bitBufferLength = 0;
 int writtenChars = 0;
+ boolean closed = false;
 
 @Override
 public void write(int b) throws IOException {
@@ -667,6 +668,10 @@ public void flush() throws IOException {
 
 @Override
 public void close() throws IOException {
+ if (closed) {
+ return;
+ }
+ closed = true;
 if (bitBufferLength> 0) {
 int charIndex = (bitBuffer << (alphabet.bitsPerChar - bitBufferLength)) & alphabet.mask;
 out.write(alphabet.encode(charIndex));
@@ -677,6 +682,7 @@ public void close() throws IOException {
 writtenChars++;
 }
 }
+ bitBufferLength = 0;
 }
 out.close();
 }
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