diff --git a/truffle/com.oracle.truffle.api.test/src/com/oracle/truffle/api/source/SourceTest.java b/truffle/com.oracle.truffle.api.test/src/com/oracle/truffle/api/source/SourceTest.java
index bbcefe773aca..5f0fe0bccd75 100644
--- a/truffle/com.oracle.truffle.api.test/src/com/oracle/truffle/api/source/SourceTest.java
+++ b/truffle/com.oracle.truffle.api.test/src/com/oracle/truffle/api/source/SourceTest.java
@@ -153,4 +153,30 @@ public void literalSources() throws IOException {
         assertEquals(literal.getReader().read(buffer), code.length());
         assertEquals(new String(buffer), code);
     }
+
+    @Test
+    public void clientManagedSourceChange() throws IOException {
+        final String path = "test.input";
+        final String code1 = "test\ntest";
+        final String code2 = "test\ntest\nlonger\ntest";
+        final Source source1 = Source.fromFileName(code1, path);
+        assertEquals(source1.getCode(), code1);
+        assertEquals(source1.getLineNumber(code1.length() - 1), 2);
+        final Source source2 = Source.fromFileName(code2, path);
+        assertEquals(source2.getCode(), code2);
+        assertEquals(source2.getLineNumber(code2.length() - 1), 4);
+    }
+
+    @Test
+    public void clientManagedSourceChangeAbsolute() throws IOException {
+        final String path = new File("test.input").getAbsolutePath();
+        final String code1 = "test\ntest";
+        final String code2 = "test\ntest\nlonger\ntest";
+        final Source source1 = Source.fromFileName(code1, path);
+        assertEquals(source1.getCode(), code1);
+        assertEquals(source1.getLineNumber(code1.length() - 1), 2);
+        final Source source2 = Source.fromFileName(code2, path);
+        assertEquals(source2.getCode(), code2);
+        assertEquals(source2.getLineNumber(code2.length() - 1), 4);
+    }
 }
diff --git a/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/source/Source.java b/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/source/Source.java
index f872f98f5a25..ffe1dca2b172 100644
--- a/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/source/Source.java
+++ b/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/source/Source.java
@@ -219,15 +219,16 @@ public static Source fromFileName(CharSequence chars, String fileName) throws IO
             if (source == null) {
                 source = new ClientManagedFileSource(file, fileName, path, chars);
                 nameToSource.put(path, new WeakReference<>(source));
+                return source;
             }
-        } else if (source instanceof ClientManagedFileSource) {
+        }
+        if (source instanceof ClientManagedFileSource) {
             final ClientManagedFileSource modifiableSource = (ClientManagedFileSource) source;
             modifiableSource.setCode(chars);
             return modifiableSource;
         } else {
             throw new IOException("Attempt to modify contents of a file Source");
         }
-        return source;
     }
 
     /**
@@ -1052,6 +1053,7 @@ private static final class ClientManagedFileSource extends Source implements Clo
         }
 
         void setCode(CharSequence chars) {
+            clearTextMap();
             this.code = chars.toString();
         }