diff --git a/lib/polyfinf.gi b/lib/polyfinf.gi
index 04acdb184b..289eb2c4d8 100644
--- a/lib/polyfinf.gi
+++ b/lib/polyfinf.gi
@@ -104,7 +104,11 @@ local   br,  ind,  c,  facs,  deg,  px,  pow,  cyc,  gcd,d,powc,fc,fam;
   #px  := LaurentPolynomialByExtRepNC(
   #	      FamilyObj(f), [One(br)],1, ind );
   #  pow := px;
-  px:=ImmutableVector(br, [Zero(br),-One(br)]);
+  if IsFinite(br) and IsField(br) and Size(br)>MAXSIZE_GF_INTERNAL then
+    px:=Immutable([Zero(br),-One(br)]);
+  else
+    px:=ImmutableVector(br, [Zero(br),-One(br)]);
+  fi;
   powc:=-px;
   fc:=CoefficientsOfLaurentPolynomial(f)[1];
   fam:=FamilyObj(One(br));
diff --git a/lib/ratfun1.gi b/lib/ratfun1.gi
index 1d7ca3d9dd..234a171672 100644
--- a/lib/ratfun1.gi
+++ b/lib/ratfun1.gi
@@ -42,7 +42,13 @@ local f,typ,lc;
   
   # slightly better to do this after the Length has been determined
   if IsFFECollection(coeff) and IS_PLIST_REP(coeff) then
-    coeff := ImmutableVector(DefaultRing(coeff), coeff);
+    f:=DefaultRing(coeff);
+    if IsFinite(f) and Size(f)>MAXSIZE_GF_INTERNAL then
+      # do not pack Zmodnz objects into vectors
+      coeff := Immutable(coeff);
+    else
+      coeff := ImmutableVector(f, coeff);
+    fi;
   fi;