diff --git a/lib/wordlett.gi b/lib/wordlett.gi
index 73ca73da1c..0456d758a4 100644
--- a/lib/wordlett.gi
+++ b/lib/wordlett.gi
@@ -165,7 +165,7 @@ local  i,r,elm,len,g,h,e;
   Add(r,e);
 
   LETTER_WORD_EREP_CACHE[LETTER_WORD_EREP_CACHEPOS]:=w;
-  LETTER_WORD_EREP_CACHEVAL[LETTER_WORD_EREP_CACHEPOS]:=Immutable(r);
+  LETTER_WORD_EREP_CACHEVAL[LETTER_WORD_EREP_CACHEPOS]:=MakeImmutable(r);
   LETTER_WORD_EREP_CACHEPOS:=(LETTER_WORD_EREP_CACHEPOS mod 3)+1;
   return r;
 end);
diff --git a/tst/testinstall/wordrep.tst b/tst/testinstall/wordrep.tst
index 6883949eaa..c8844d876c 100644
--- a/tst/testinstall/wordrep.tst
+++ b/tst/testinstall/wordrep.tst
@@ -304,4 +304,11 @@ gap> e1=e2;
 true
 
 #
-gap> STOP_TEST("wordrep.tst", 1);
+gap> f:= FreeGroup(IsLetterWordsFamily,4);;
+gap> IsMutable(ExtRepOfObj(f.1));
+false
+gap> IsMutable(ExtRepOfObj(f.1));
+false
+
+#
+gap> STOP_TEST("wordrep.tst");