diff --git a/lib/openai/internal/util.rb b/lib/openai/internal/util.rb
index f463559f..d028d8a4 100644
--- a/lib/openai/internal/util.rb
+++ b/lib/openai/internal/util.rb
@@ -428,11 +428,11 @@ def close
             @stream.to_a.join
           in Integer
             @buf << @stream.next while @buf.length < max_len
-            @buf.slice!(..max_len)
+            @buf.slice!(0, max_len)
           end
         rescue StopIteration
           @stream = nil
-          @buf.slice!(0..)
+          @buf.empty? ? nil : @buf.slice!(0..)
         end
 
         # @api private
@@ -442,21 +442,23 @@ def close
         #
         # @return [String, nil]
         def read(max_len = nil, out_string = nil)
-          case @stream
-          in nil
-            nil
-          in IO | StringIO
-            @stream.read(max_len, out_string)
-          in Enumerator
-            read = read_enum(max_len)
-            case out_string
-            in String
-              out_string.replace(read)
+          read =
+            case @stream
             in nil
-              read
+              nil
+            in IO | StringIO
+              return @stream.read(max_len, out_string).tap(&@blk)
+            in Enumerator
+              read_enum(max_len)
             end
-          end
-            .tap(&@blk)
+
+          case out_string
+          in String
+            out_string.replace(read || "")
+            read.nil? ? nil : out_string
+          in nil
+            read
+          end.tap(&@blk)
         end
 
         # @api private
diff --git a/test/openai/internal/util_test.rb b/test/openai/internal/util_test.rb
index 8566246b..9f52ee4d 100644
--- a/test/openai/internal/util_test.rb
+++ b/test/openai/internal/util_test.rb
@@ -329,6 +329,58 @@ def test_copy_read
     end
   end
 
+  def test_read_respects_max_len_for_enumerator
+    input =
+      Enumerator.new do |y|
+        y << "ab"
+        y << "cd"
+        y << "ef"
+      end
+
+    # rubocop:disable Lint/EmptyBlock
+    adapter = OpenAI::Internal::Util::ReadIOAdapter.new(input) {}
+    # rubocop:enable Lint/EmptyBlock
+
+    assert_equal("abc", adapter.read(3))
+    assert_equal("def", adapter.read(3))
+    assert_nil(adapter.read(3))
+  end
+
+  def test_read_clears_out_string_at_eof_for_enumerator
+    input =
+      Enumerator.new do |y|
+        y << "ab"
+        y << "cd"
+        y << "ef"
+      end
+
+    # rubocop:disable Lint/EmptyBlock
+    adapter = OpenAI::Internal::Util::ReadIOAdapter.new(input) {}
+    # rubocop:enable Lint/EmptyBlock
+    out = +"seed"
+
+    assert_same(out, adapter.read(3, out))
+    assert_equal("abc", out)
+    assert_same(out, adapter.read(3, out))
+    assert_equal("def", out)
+    assert_nil(adapter.read(3, out))
+    assert_equal("", out)
+  end
+
+  def test_copy_read_for_enumerator_exactly_on_copy_stream_boundary
+    body = "a" * 16_384
+    input = Enumerator.new { _1 << body }
+    io = StringIO.new
+
+    # rubocop:disable Lint/EmptyBlock
+    adapter = OpenAI::Internal::Util::ReadIOAdapter.new(input) {}
+    # rubocop:enable Lint/EmptyBlock
+
+    IO.copy_stream(adapter, io)
+
+    assert_equal(body, io.string)
+  end
+
   def test_copy_write
     cases = {
       StringIO.new => "",