diff --git a/modules/SequencesExt.tla b/modules/SequencesExt.tla
index 2183f30..b828acb 100644
--- a/modules/SequencesExt.tla
+++ b/modules/SequencesExt.tla
@@ -167,7 +167,8 @@ SelectInSeq(seq, Test(_)) ==
 (* FALSE for all elements.                                               *)
 (*************************************************************************)
 SelectInSubSeq(seq, from, to, Test(_)) ==
-  SelectInSeq(SubSeq(seq, from, to), Test)
+  LET I == { i \in from..to : Test(seq[i]) }
+  IN IF I # {} THEN Min(I) ELSE 0
 
 (*************************************************************************)
 (* Selects the index of the last element such that Test(seq[i]) is true  *)
@@ -183,7 +184,8 @@ SelectLastInSeq(seq, Test(_)) ==
 (* FALSE for all elements.                                               *)
 (*************************************************************************)
 SelectLastInSubSeq(seq, from, to, Test(_)) ==
-  SelectLastInSeq(SubSeq(seq, from, to), Test)
+  LET I == { i \in from..to : Test(seq[i]) }
+  IN IF I # {} THEN Max(I) ELSE 0
 
 -----------------------------------------------------------------------------
 
diff --git a/tests/SequencesExtTests.tla b/tests/SequencesExtTests.tla
index 7ac3f94..3ab2732 100644
--- a/tests/SequencesExtTests.tla
+++ b/tests/SequencesExtTests.tla
@@ -447,6 +447,26 @@ ASSUME AssertEq(SelectLastInSubSeq(<<>>, 1, Len(<<>>), Op), 0)
 ASSUME AssertEq(SelectLastInSubSeq(<<1,1,2>>  , 1, 3, LAMBDA e : e = 1), 2)
 ASSUME AssertEq(SelectLastInSubSeq(<<1,1,2,2>>, 2, 4, LAMBDA e : e = 2), 4)
 
+SelectInSubSeqPure(seq, from, to, Test(_)) ==
+  LET I == { i \in from..to : Test(seq[i]) }
+  IN IF I # {} THEN CHOOSE i \in I : \A j \in I : i <= j ELSE 0
+
+SelectLastInSubSeqPure(seq, from, to, Test(_)) ==
+  LET I == { i \in from..to : Test(seq[i]) }
+  IN IF I # {} THEN CHOOSE i \in I : \A j \in I : i >= j ELSE 0
+
+ASSUME AssertEq(SelectInSubSeq(<<1,1,2>>, 2, 3, LAMBDA e : e = 1), SelectInSubSeqPure(<<1,1,2>>, 2, 3, LAMBDA e : e = 1))
+ASSUME AssertEq(SelectInSubSeq(<<1,1,2,2>>, 2, 4, LAMBDA e : e = 2), SelectInSubSeqPure(<<1,1,2,2>>, 2, 4, LAMBDA e : e = 2))
+ASSUME AssertEq(SelectLastInSubSeq(<<1,1,2,2>>, 2, 4, LAMBDA e : e = 2), SelectLastInSubSeqPure(<<1,1,2,2>>, 2, 4, LAMBDA e : e = 2))
+
+ASSUME \A seq \in BoundedSeq(1..3, 4):
+         \A from \in 1..Len(seq) + 1, to \in 0..Len(seq):
+           \A v \in 1..3:
+             /\ AssertEq(SelectInSubSeq(seq, from, to, LAMBDA e : e = v),
+                         SelectInSubSeqPure(seq, from, to, LAMBDA e : e = v))
+             /\ AssertEq(SelectLastInSubSeq(seq, from, to, LAMBDA e : e = v),
+                         SelectLastInSubSeqPure(seq, from, to, LAMBDA e : e = v))
+
 -----------------------------------------------------------------------------
 
 ASSUME AssertEq(Suffixes(<<>>), {<<>>})