diff --git a/jansi/src/main/java/org/fusesource/jansi/AnsiPrintStream.java b/jansi/src/main/java/org/fusesource/jansi/AnsiPrintStream.java
index 4cea3f2f..d1bbf370 100644
--- a/jansi/src/main/java/org/fusesource/jansi/AnsiPrintStream.java
+++ b/jansi/src/main/java/org/fusesource/jansi/AnsiPrintStream.java
@@ -74,7 +74,7 @@ public AnsiPrintStream(PrintStream ps) { // expected diff with AnsiOutputStream.
     private static final int SECOND_CHARSET1_CHAR = ')';
 
     @Override
-    protected boolean filter(int data) { // expected diff with AnsiOutputStream.java
+    protected synchronized boolean filter(int data) { // expected diff with AnsiOutputStream.java
         switch (state) {
             case LOOKING_FOR_FIRST_ESC_CHAR:
                 if (data == FIRST_ESC_CHAR) {