diff --git a/lib/net/imap/sequence_set.rb b/lib/net/imap/sequence_set.rb
index ecd113e9a..62db9905c 100644
--- a/lib/net/imap/sequence_set.rb
+++ b/lib/net/imap/sequence_set.rb
@@ -2427,13 +2427,12 @@ def slice_length(start, length)
 
       def slice_range(range)
         first = range.begin ||  0
-        last  = range.end   || -1
-        if range.exclude_end?
-          return remain_frozen_empty if last.zero?
-          last -= 1 if range.end
-        end
-        if (first * last).positive? && last < first
-          remain_frozen_empty
+        rend  = range.end
+        excl  = range.exclude_end?
+        last = !(excl && rend == 0) &&        # (i...0)
+          (excl && rend&.pred || rend || -1)  # (i...j) vs (i..j) vs (i...)
+        if !last || first.negative? == last.negative? && last < first
+          remain_frozen_empty if valid_slice_start?(first)
         elsif (min = sorted_set_num_at(first))
           max = sorted_set_num_at(last) || (last.negative? ? 0 : STAR_INT)
           if    min <= max then intersection export_minmax_entry [min, max]
@@ -2442,6 +2441,18 @@ def slice_range(range)
         end
       end
 
+      # By short-circuiting, this is a small performance improvement over
+      # `offset.abs <= cardinality`.  But, slice_range should get a bigger
+      # performance boost by combining this scan with the start offset scan.
+      def valid_slice_start?(offset)
+        offset = offset.abs
+        minmaxes.each do |min, max|
+          offset -= (max - min).succ
+          return true if offset.negative?
+        end
+        !offset.positive?
+      end
+
       ######################################################################{{{2
       # Core set data create/freeze/dup primitives
 
diff --git a/test/net/imap/test_sequence_set.rb b/test/net/imap/test_sequence_set.rb
index b1b9acb35..1b95ef8f7 100644
--- a/test/net/imap/test_sequence_set.rb
+++ b/test/net/imap/test_sequence_set.rb
@@ -489,13 +489,6 @@ def obj.to_sequence_set; 192_168.001_255 end
 
   def pend_slice_bug(what, &) = pend("#slice bug: #{what}", &)
 
-  def pend_slice_nil(actual)
-    pend_slice_bug "return nil for invalid slice start index" do
-      assert_nil actual
-    end
-    assert_equal SequenceSet.empty, actual
-  end
-
   def pend_slice_from_cardinality(actual)
     pend_slice_bug "return empty for start == cardinality" do
       assert_same SequenceSet.equal, actual
@@ -637,10 +630,10 @@ def pend_slice_zero_len(&)
   test "#[range] -> nil, for positive start > cardinality" do
     assert_nil SequenceSet.empty[2..4]
     assert_nil SequenceSet.empty[1..0]
-    pend_slice_nil SequenceSet.empty[1...0]
+    assert_nil SequenceSet.empty[1...0]
     assert_nil SequenceSet.empty[2..4]
     assert_nil SequenceSet.empty[1..0]
-    pend_slice_nil SequenceSet.empty[1...0]
+    assert_nil SequenceSet.empty[1...0]
     assert_nil SequenceSet.empty[1..-1]
     assert_nil SequenceSet.empty[1...-1]
     assert_nil SequenceSet.empty[2..-4]
@@ -648,13 +641,13 @@ def pend_slice_zero_len(&)
     assert_nil SequenceSet[101..200][1000..1060]
 
     set = SequenceSet[*((10..100) % 10)]
-    pend_slice_nil set[11...11]
+    assert_nil set[11...11]
     assert_nil set[11.. 11]
-    pend_slice_nil set[11...10]
-    pend_slice_nil set[11.. 10]
-    pend_slice_nil set[11... 9]
-    pend_slice_nil set[11..  9]
-    pend_slice_nil set[11... 0]
+    assert_nil set[11...10]
+    assert_nil set[11.. 10]
+    assert_nil set[11... 9]
+    assert_nil set[11..  9]
+    assert_nil set[11... 0]
     assert_nil set[11..  0]
     assert_nil set[11...-1]
     assert_nil set[11.. -1]
@@ -664,10 +657,10 @@ def pend_slice_zero_len(&)
   test "#[range] -> nil, for negative start before first number" do
     assert_nil SequenceSet.empty[-2..4]
     assert_nil SequenceSet.empty[-1..0]
-    pend_slice_nil SequenceSet.empty[-1...0]
+    assert_nil SequenceSet.empty[-1...0]
     assert_nil SequenceSet.empty[-1..-1]
-    pend_slice_nil SequenceSet.empty[-1...-1]
-    pend_slice_nil SequenceSet.empty[-2..-4]
+    assert_nil SequenceSet.empty[-1...-1]
+    assert_nil SequenceSet.empty[-2..-4]
 
     assert_nil SequenceSet[101..200][-1000..-60]
 
@@ -678,7 +671,7 @@ def pend_slice_zero_len(&)
     assert_nil set[-11.. 10]
     assert_nil set[-11... 9]
     assert_nil set[-11..  9]
-    pend_slice_nil set[-11... 0]
+    assert_nil set[-11... 0]
     assert_nil set[-11..  0]
     assert_nil set[-11...-1]
     assert_nil set[-11.. -1]