diff --git a/lib/pp.rb b/lib/pp.rb
index 798a4f4..1a6bf26 100644
--- a/lib/pp.rb
+++ b/lib/pp.rb
@@ -82,6 +82,9 @@ def PP.width_for(out)
       _, width = out.winsize
     rescue LoadError, NoMethodError, SystemCallError
     end
+    # winsize can report 0 for a non-tty or constrained device; treat that
+    # like a missing width so we fall back to COLUMNS / 80 instead of -1.
+    width = nil unless width&.nonzero?
     (width || ENV['COLUMNS']&.to_i&.nonzero? || 80) - 1
   end
 
@@ -220,7 +223,8 @@ def pp(obj)
     #
     #   group(1, '#<' + obj.class.name, '>') { ... }
     def object_group(obj, &block) # :yield:
-      group(1, '#<' + obj.class.name, '>', &block)
+      # Anonymous classes have a nil #name; #to_s still yields a usable label.
+      group(1, '#<' + (obj.class.name || obj.class.to_s), '>', &block)
     end
 
     # A convenience method, like object_group, but also reformats the Object's
diff --git a/test/test_pp.rb b/test/test_pp.rb
index 922ed37..9040eba 100644
--- a/test/test_pp.rb
+++ b/test/test_pp.rb
@@ -46,6 +46,20 @@ def test_range
     assert_equal("false..false\n", PP.pp(false..false, "".dup))
     assert_equal("nil..nil\n", PP.pp(nil..nil, "".dup))
   end
+
+  def test_width_for_zero_winsize
+    out = Object.new
+    def out.winsize; [24, 0]; end
+    assert_equal(79, PP.width_for(out))
+  end
+
+  def test_object_group_anonymous_class
+    obj = Class.new.new
+    q = PP.new("".dup)
+    q.object_group(obj) { q.text "x" }
+    q.flush
+    assert_match(/\A#<#<Class:0x[0-9a-f]+>x>\z/, q.output)
+  end
 end
 
 class HasInspect