diff --git a/lib/bingo.rb b/lib/bingo.rb
index 53ba5f5..58367cf 100644
--- a/lib/bingo.rb
+++ b/lib/bingo.rb
@@ -138,7 +138,10 @@ module Bingo
 
     module_function
 
+    # Input may arrive tagged UTF-8 (aws-sdk bodies are plain StringIOs), and
+    # comparing that with binary literals raises, so look at raw bytes.
     def sniff(bytes)
+      bytes = bytes.b
       return 'jpg'  if bytes.start_with?("\xFF\xD8\xFF".b)
       return 'png'  if bytes.start_with?("\x89PNG\r\n\x1A\n".b)
       return 'webp' if bytes[0, 4] == 'RIFF' && bytes[8, 4] == 'WEBP'
@@ -175,6 +178,7 @@ module Bingo
     end
 
     def build_variants(key, bytes)
+      bytes = bytes.b
       ext = sniff(bytes) or raise Error, 'not an image'
       WIDTHS.each { |w| S3.put(variant_key(key, w), resize(bytes, ext, w), content_type: TYPES['webp']) }
       true
@@ -198,6 +202,8 @@ module Bingo
       out.b
     rescue Errno::ENOENT
       raise Error, 'ImageMagick (convert) not installed'
+    rescue Errno::EPIPE, IOError => e # convert exited before reading all input
+      raise Error, "convert: #{e.class}"
     end
 
     # Photos are served byte-for-byte, so drop EXIF/XMP/IPTC/text metadata:
@@ -276,7 +282,7 @@ module Bingo
             raise Error, 'too many redirects' if redirects.zero?
             return fetch(URI.join(uri, res['location']).to_s, redirects: redirects - 1)
           when Net::HTTPSuccess
-            body = +''
+            body = +''.b
             res.read_body do |chunk|
               body << chunk
               raise Error, 'image too large (max 8 MB)' if body.bytesize > MAX_BYTES
diff --git a/lib/bingo_admin.rb b/lib/bingo_admin.rb
index 63ac4ac..9a4b93a 100644
--- a/lib/bingo_admin.rb
+++ b/lib/bingo_admin.rb
@@ -162,8 +162,14 @@ module BingoAdmin
     # Regenerate resized variants from the originals already in the bucket.
     app.post '/admin/bingo/photos/rebuild' do
       dcs = Bingo::Datacenter.exclude(photo_key: nil).all
-      dcs.each { |dc| Bingo::Photo.rebuild(dc) }
-      failed = dcs.reject(&:photo_variants).map(&:slug)
+      errors = {}
+      dcs.each do |dc|
+        Bingo::Photo.rebuild(dc)
+      rescue StandardError => e # one bad object must not abort the batch
+        errors[dc.slug] = "#{e.class}: #{e.message.lines.first&.strip}"
+        $logger.error("bingo: rebuild #{dc.slug}: #{e.class}: #{e.message}")
+      end
+      failed = dcs.reject(&:photo_variants).map { |dc| errors[dc.slug] ? "#{dc.slug} (#{errors[dc.slug]})" : dc.slug }
       session[:bingo_flash] = "Rebuilt #{dcs.size - failed.size}/#{dcs.size}.#{" Failed: #{failed.join(', ')}" if failed.any?}"
       redirect '/admin/bingo'
     end
diff --git a/lib/s3.rb b/lib/s3.rb
index 339ed84..ca74d7a 100644
--- a/lib/s3.rb
+++ b/lib/s3.rb
@@ -41,7 +41,7 @@ module S3
   end
 
   def get(key)
-    client.get_object(bucket: bucket, key: key).body.read
+    client.get_object(bucket: bucket, key: key).body.read.b # body is a UTF-8 StringIO
   end
 
   def exists?(key)
diff --git a/test/bingo_test.rb b/test/bingo_test.rb
index 87f5578..bdd5ce2 100644
--- a/test/bingo_test.rb
+++ b/test/bingo_test.rb
@@ -170,6 +170,23 @@ class BingoTest < Minitest::Test
     assert_equal '480x240', dims
   end
 
+  def test_sniff_accepts_utf8_tagged_bytes
+    assert_equal 'jpg', Bingo::Photo.sniff(JPEG.dup.force_encoding('UTF-8'))
+  end
+
+  def test_rebuild_from_utf8_s3_body
+    skip 'ImageMagick not available' unless system(Bingo::Photo::CONVERT, '-version', out: File::NULL, err: File::NULL)
+    png, = Open3.capture2(Bingo::Photo::CONVERT, '-size', '800x600', 'gradient:red-blue', 'png:-', binmode: true)
+    Aws.config[:s3] = { stub_responses: { get_object: { body: png.dup.force_encoding('UTF-8') } } }
+    S3.instance_variable_set(:@client, nil)
+    @dcs[0].update(photo_key: 'bingo/dc-1-0123abcd.png')
+    Bingo::Photo.rebuild(@dcs[0])
+    assert @dcs[0].refresh.photo_variants
+  ensure
+    Aws.config[:s3] = { stub_responses: true }
+    S3.instance_variable_set(:@client, nil)
+  end
+
   def test_photo_rejects_non_images
     assert_raises(Bingo::Photo::Error) { Bingo::Photo.store('dc-1', '<html>') }
   end