diff --git a/src/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriter.java b/src/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriter.java
index 2f6c1db..e69193f 100644
--- a/src/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriter.java
+++ b/src/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriter.java
@@ -77,7 +77,9 @@ public class SourceMapWriter {
 
         // sourceRoot
         if( sourceRoot != null && !sourceRoot.isEmpty() ) {
-            appendJsonField( out, "sourceRoot", sourceRoot );
+            out.append( ",\n" );
+            appendJsonField( out, "sourceRoot", "" );
+            appendQuoteString( out, sourceRoot );
         }
 
         // the source file names
diff --git a/test/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriterTest.java b/test/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriterTest.java
index aa2765e..15d6a13 100644
--- a/test/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriterTest.java
+++ b/test/de/inetsoftware/jwebassembly/sourcemap/SourceMapWriterTest.java
@@ -27,4 +27,25 @@ public class SourceMapWriterTest {
                         "}";
         assertEquals( expected, generate.toString() );
     }
+
+    @Test
+    public void sourceRootNotNull() throws IOException {
+        SourceMapWriter map = new SourceMapWriter( "../../src/main/java/" );
+
+        map.addMapping( new SourceMapping( 0, 1, "Test1.java" ) );
+        map.addMapping( new SourceMapping( 5, 2, "Test1.java" ) );
+        map.addMapping( new SourceMapping( 0, 4, "Test2.java" ) );
+        map.addMapping( new SourceMapping( 5, 9, "Test2.java" ) );
+
+        StringBuilder generate = new StringBuilder();
+        map.generate( generate );
+        String expected = "{\n" +
+                "\"version\":3,\n" +
+                "\"sourceRoot\":\"../../src/main/java/\",\n" +
+                "\"sources\":[\"Test1.java\",\"Test2.java\"],\n" +
+                "\"names\":[],\n" +
+                "\"mappings\":\"AAAA,KACA,LCEA,KAKA;\"\n" +
+                "}";
+        assertEquals( expected, generate.toString() );
+    }
 }