diff --git a/org.hl7.fhir.publisher.core/src/main/java/org/hl7/fhir/igtools/publisher/FSHRunner.java b/org.hl7.fhir.publisher.core/src/main/java/org/hl7/fhir/igtools/publisher/FSHRunner.java
index 63c69803b..8bff7d2cc 100644
--- a/org.hl7.fhir.publisher.core/src/main/java/org/hl7/fhir/igtools/publisher/FSHRunner.java
+++ b/org.hl7.fhir.publisher.core/src/main/java/org/hl7/fhir/igtools/publisher/FSHRunner.java
@@ -20,6 +20,8 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
+import java.util.function.Consumer;
 import java.util.StringJoiner;
 
 public class FSHRunner {
@@ -63,7 +65,7 @@ protected void runFsh(File file, Publisher.IGBuildMode mode) throws IOException
         log("Run Sushi on "+file.getAbsolutePath());
         DefaultExecutor exec = new DefaultExecutor();
         exec.setExitValue(0);
-        MySushiHandler pumpHandler = new MySushiHandler();
+        MySushiHandler pumpHandler = new MySushiHandler(this::log);
         PumpStreamHandler pump = new PumpStreamHandler(pumpHandler);
         exec.setStreamHandler(pump);
         exec.setWorkingDirectory(file);
@@ -96,11 +98,12 @@ protected void runFsh(File file, Publisher.IGBuildMode mode) throws IOException
             log("Exception: "+ioex.getMessage());
             throw ioex;
         }
-        if (pumpHandler.errorCount > 0) {
+        if (pumpHandler.getErrorCount() > 0) {
             throw new IOException("Sushi failed with errors. Complete output from running Sushi : " + pumpHandler.getBufferString());
         }
     }
 
+
     @Nonnull
     protected CommandLine getDefaultCommandLine(String fshVersion, Publisher.IGBuildMode mode) {
         final List<String> sushiCommandList = getSushiCommandList(fshVersion, mode);
@@ -147,40 +150,45 @@ protected String getSushiCommandString(String fshVersion, Publisher.IGBuildMode
         }
         return stringJoiner.toString();
     }
-    public class MySushiHandler extends OutputStream {
+  
+    public static class MySushiHandler extends OutputStream {
 
-        private byte[] buffer;
-        private int length;
+        private final StringBuilder buffer;
         private int errorCount = -1;
+        private final Consumer<String> outputConsumer;
 
-        public MySushiHandler() {
-            buffer = new byte[256];
+        public MySushiHandler(final Consumer<String> outputConsumer) {
+            buffer = new StringBuilder(256);
+            this.outputConsumer = Objects.requireNonNull(outputConsumer);
         }
 
         public String getBufferString() {
-            return new String(this.buffer, 0, length);
+            return this.buffer.toString();
         }
 
         private boolean passSushiFilter(String s) {
-            if (Utilities.noString(s))
+            if (Utilities.noString(s) || s.isBlank())
                 return false;
             return true;
         }
 
         @Override
         public void write(int b) throws IOException {
-            buffer[length] = (byte) b;
-            length++;
+            this.buffer.appendCodePoint(b);
             if (b == 10) { // eoln
-                String s = new String(buffer, 0, length);
+                final String s = this.getBufferString();
                 if (passSushiFilter(s)) {
-                    log("Sushi: "+ StringUtils.stripEnd(s, null));
+                    this.outputConsumer.accept("Sushi: "+ StringUtils.stripEnd(s, null));
                     if (s.trim().startsWith("Errors:")) {
                         errorCount = Integer.parseInt(s.substring(10).trim());
                     }
                 }
-                length = 0;
+                this.buffer.setLength(0);
             }
         }
+
+        protected int getErrorCount() {
+            return errorCount;
+        }
     }
 }
diff --git a/org.hl7.fhir.publisher.core/src/test/java/org/hl7/fhir/igtools/publisher/FSHRunnerTest.java b/org.hl7.fhir.publisher.core/src/test/java/org/hl7/fhir/igtools/publisher/FSHRunnerTest.java
new file mode 100644
index 000000000..e6fcf76e8
--- /dev/null
+++ b/org.hl7.fhir.publisher.core/src/test/java/org/hl7/fhir/igtools/publisher/FSHRunnerTest.java
@@ -0,0 +1,72 @@
+package org.hl7.fhir.igtools.publisher;
+
+import org.junit.jupiter.api.Test;
+
+import javax.annotation.Nonnull;
+import java.io.IOException;
+import java.util.function.Consumer;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Tests for the {@link FSHRunner} class.
+ *
+ * @author Quentin Ligier
+ **/
+class FSHRunnerTest {
+
+    @Test
+    void testMySushiHandler() throws IOException {
+
+        final StringBuilder stringBuilder = new StringBuilder(512);
+        final FSHRunner.MySushiHandler mySushiHandler = getMySushiHandler(stringBuilder);
+        for (final int codePoint : "1234".codePoints().toArray()) {
+            mySushiHandler.write(codePoint);
+        }
+        assertEquals("1234", mySushiHandler.getBufferString());
+        assertEquals(0, stringBuilder.length());
+        mySushiHandler.write(10); // EOL
+        assertEquals("", mySushiHandler.getBufferString());
+        assertEquals("Sushi: 1234", stringBuilder.toString());
+    }
+
+    @Nonnull
+    private static FSHRunner.MySushiHandler getMySushiHandler(StringBuilder stringBuilder) {
+        final Consumer<String> stringConsumer = stringBuilder::append;
+        return new FSHRunner.MySushiHandler(stringConsumer);
+    }
+
+    @Test
+    public void testMySushiHandlerLongStrings() throws IOException {
+        final StringBuilder stringBuilder = new StringBuilder(512);
+        final FSHRunner.MySushiHandler mySushiHandler = getMySushiHandler(stringBuilder);
+        // Test long strings, larger than the initial buffer size
+        final int largeLength = 500;
+        for (int i = 0; i < largeLength; ++i) {
+            mySushiHandler.write('a');
+        }
+        assertEquals(largeLength, mySushiHandler.getBufferString().length());
+        assertEquals(0, stringBuilder.length());
+        mySushiHandler.write(10); // EOL
+        assertEquals("", mySushiHandler.getBufferString());
+        assertEquals(largeLength + 7, stringBuilder.toString().length());
+    }
+
+    @Test
+    void testMySushiHandlerErrors() throws IOException {
+
+        final StringBuilder stringBuilder = new StringBuilder(512);
+        final FSHRunner.MySushiHandler mySushiHandler = getMySushiHandler(stringBuilder);
+        for (final int codePoint : "1234".codePoints().toArray()) {
+            mySushiHandler.write(codePoint);
+        }
+        mySushiHandler.write(10); // EOL
+        for (final int codePoint : "  Errors: 13".codePoints().toArray()) {
+            mySushiHandler.write(codePoint);
+        }
+        mySushiHandler.write(10); // EOL
+        assertEquals("", mySushiHandler.getBufferString());
+        assertEquals("Sushi: 1234Sushi:   Errors: 13", stringBuilder.toString());
+        assertEquals(13, mySushiHandler.getErrorCount());
+    }
+}