diff --git a/lib/ghomperm.gi b/lib/ghomperm.gi
index d8d72c9075..d2d28d318f 100644
--- a/lib/ghomperm.gi
+++ b/lib/ghomperm.gi
@@ -1928,7 +1928,8 @@ end);
 InstallMethod( IsomorphismPermGroup,
     "perm groups",
     true,
-    [ IsPermGroup ], 0,
+    [ IsPermGroup ],
+    SUM_FLAGS,
     IdentityMapping );
 
 
diff --git a/tst/testinstall/grpperm.tst b/tst/testinstall/grpperm.tst
index 0484193cf8..dc23140f82 100644
--- a/tst/testinstall/grpperm.tst
+++ b/tst/testinstall/grpperm.tst
@@ -77,4 +77,6 @@ gap> IsSolvable(G);
 false
 gap> Length(MinimalGeneratingSet(G));
 2
+gap> IsomorphismPermGroup(G) = IdentityMapping(G);
+true
 gap> STOP_TEST( "grpperm.tst", 1);