diff --git a/lib/gitlab/encoding_helper.rb b/lib/gitlab/encoding_helper.rb
index 8ac756a0b6ac157cea5cb6a7041b7fb7c2718076..c50417f4d4f5839d282497ab7291461ad6bf9e72 100644
--- a/lib/gitlab/encoding_helper.rb
+++ b/lib/gitlab/encoding_helper.rb
@@ -24,7 +24,7 @@ module Gitlab
 
       # return message if message type is binary
       detect = CharlockHolmes::EncodingDetector.detect(message)
-      return message.force_encoding("BINARY") if all_binary?(message, detect)
+      return message.force_encoding("BINARY") if detect_binary?(message, detect)
 
       if detect && detect[:encoding] && detect[:confidence] > ENCODING_CONFIDENCE_THRESHOLD
         # force detected encoding if we have sufficient confidence.
@@ -38,17 +38,17 @@ module Gitlab
       "--broken encoding: #{encoding}"
     end
 
-    def all_binary?(data, detect = nil)
+    def detect_binary?(data, detect = nil)
       detect ||= CharlockHolmes::EncodingDetector.detect(data)
-      detect && detect[:type] == :binary
+      detect && detect[:type] == :binary && detect[:confidence] == 100
     end
 
-    def libgit2_binary?(data)
+    def detect_libgit2_binary?(data)
       # EncodingDetector checks the first 1024 * 1024 bytes for NUL byte, libgit2 checks
       # only the first 8000 (https://github.com/libgit2/libgit2/blob/2ed855a9e8f9af211e7274021c2264e600c0f86b/src/filter.h#L15),
       # which is what we use below to keep a consistent behavior.
       detect = CharlockHolmes::EncodingDetector.new(8000).detect(data)
-      all_binary?(data, detect)
+      detect && detect[:type] == :binary
     end
 
     def encode_utf8(message)
diff --git a/lib/gitlab/git/blob.rb b/lib/gitlab/git/blob.rb
index e5391b8bf8a0d0725e54b8c609a7d31b591f17e6..8d96826f6ee616da2fc3654d4e64fc1dab5536c2 100644
--- a/lib/gitlab/git/blob.rb
+++ b/lib/gitlab/git/blob.rb
@@ -58,7 +58,7 @@ module Gitlab
         end
 
         def binary?(data)
-          EncodingHelper.libgit2_binary?(data)
+          EncodingHelper.detect_libgit2_binary?(data)
         end
 
         private
diff --git a/lib/gitlab/git/diff.rb b/lib/gitlab/git/diff.rb
index b3237d5496abb07d90fa606cf982d7dcfac57f9f..a23c8cf0dd1188fbca507d02723f31f04371ec2f 100644
--- a/lib/gitlab/git/diff.rb
+++ b/lib/gitlab/git/diff.rb
@@ -120,6 +120,8 @@ module Gitlab
         # Return a binary diff message like:
         #
         # "Binary files a/file/path and b/file/path differ\n"
+        # This is used when we detect that a diff is binary
+        # using CharlockHolmes when Rugged treats it as text.
         def binary_message(old_path, new_path)
           "Binary files #{old_path} and #{new_path} differ\n"
         end
@@ -198,7 +200,7 @@ module Gitlab
       end
 
       def json_safe_diff
-        return @diff unless all_binary?(@diff)
+        return @diff unless detect_binary?(@diff)
 
         # the diff is binary, let's make a message for it
         Diff.binary_message(@old_path, @new_path)
diff --git a/spec/requests/api/commits_spec.rb b/spec/requests/api/commits_spec.rb
index edbfaf510c5ee7d3dd9cc27e45792fc48b0e0d5e..f663719d28c051e74a1d9f90c104a8a32b7220b1 100644
--- a/spec/requests/api/commits_spec.rb
+++ b/spec/requests/api/commits_spec.rb
@@ -673,6 +673,12 @@ describe API::Commits do
           it_behaves_like 'ref diff'
         end
       end
+
+      context 'when binary diff are treated as text' do
+        let(:commit_id) { TestEnv::BRANCH_SHA['add-pdf-text-binary'] }
+
+        it_behaves_like 'ref diff'
+      end
     end
   end