diff --git a/de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/attributes/AttrExprExpectedType.java b/de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/attributes/AttrExprExpectedType.java
index 822301048..53e90a6d7 100644
--- a/de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/attributes/AttrExprExpectedType.java
+++ b/de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/attributes/AttrExprExpectedType.java
@@ -37,7 +37,7 @@ public class AttrExprExpectedType {
             } else if (parent instanceof StmtSet) {
                 StmtSet stmtSet = (StmtSet) parent;
                 if (stmtSet.getRight() == expr) {
-                    return stmtSet.getUpdatedExpr().attrTyp();
+                    return stmtSet.getUpdatedExpr().attrTypRaw();
                 } else if (stmtSet.getUpdatedExpr() == expr) {
                     return WurstTypeUnknown.instance();
                 }
diff --git a/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/GenericsTests.java b/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/GenericsTests.java
index 1c71d5868..9fc21b2ef 100644
--- a/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/GenericsTests.java
+++ b/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/GenericsTests.java
@@ -958,6 +958,25 @@ public void genericFunctionOverload() { // #628
         );
     }
 
+    @Test
+    public void genericToIndexFieldAssignment() { // #647
+        testAssertOkLines(true,
+            "package test",
+            "native testSuccess()",
+            "class C<T>",
+            "    T x",
+            "function stringToIndex(string s) returns int",
+            "    return 42",
+            "function stringFromIndex(int i) returns string",
+            "    return \"42\"",
+            "init",
+            "    C<string> c = new C<string>",
+            "    c.x = \"42\"",
+            "    if c.x == \"42\"",
+            "        testSuccess()"
+        );
+    }
+
     @Test
     public void extensionFunc() { // #718
         testAssertOkLines(false,
diff --git a/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/LuaTranslationTests.java b/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/LuaTranslationTests.java
index 8a6d6b14c..014a3d9ce 100644
--- a/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/LuaTranslationTests.java
+++ b/de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/LuaTranslationTests.java
@@ -1373,6 +1373,25 @@ public void newGenericsStringFieldAssignmentRoundTripsInLua() throws IOException
         assertFunctionBodyContains(compiled, "testGenericStringField", "__wurst_stringFromIndex", false);
     }
 
+    @Test
+    public void legacyGenericToIndexFieldAssignmentRoundTripsInLua() {
+        test().testLua(true).executeProg().lines(
+            "package test",
+            "native testSuccess()",
+            "class C<T>",
+            "    T x",
+            "function stringToIndex(string s) returns int",
+            "    return 42",
+            "function stringFromIndex(int i) returns string",
+            "    return \"42\"",
+            "init",
+            "    C<string> c = new C<string>",
+            "    c.x = \"42\"",
+            "    if c.x == \"42\"",
+            "        testSuccess()"
+        );
+    }
+
     @Test
     public void genericOverrideChainBindsRootSlotToMostSpecificImplInLua() throws IOException {
         test().testLua(true).compilationUnits(genericOverrideReproUnits());