diff --git a/Library/Homebrew/utils/github/api.rb b/Library/Homebrew/utils/github/api.rb
index 4dc96c50d5..324986fce2 100644
--- a/Library/Homebrew/utils/github/api.rb
+++ b/Library/Homebrew/utils/github/api.rb
@@ -177,8 +177,9 @@ module GitHub
                                                        print_stderr: false
         return unless result.success?
 
-        github_username = git_credential_out[/username=(.+)/, 1]
-        github_password = git_credential_out[/password=(.+)/, 1]
+        git_credential_out.force_encoding("ASCII-8BIT")
+        github_username = git_credential_out[/^username=(.+)/, 1]
+        github_password = git_credential_out[/^password=(.+)/, 1]
         return unless github_username
 
         # Don't use passwords from the keychain unless they look like