diff --git a/xls/public/c_api.cc b/xls/public/c_api.cc
index da85cbb5b5..3f4802864c 100644
--- a/xls/public/c_api.cc
+++ b/xls/public/c_api.cc
@@ -233,6 +233,10 @@ bool xls_format_preference_from_string(const char* s, char** error_out,
     *result_out = xls_format_preference_plain_binary;
   } else if (got == "plain_hex") {
     *result_out = xls_format_preference_plain_hex;
+  } else if (got == "zero_padded_binary") {
+    *result_out = xls_format_preference_zero_padded_binary;
+  } else if (got == "zero_padded_hex") {
+    *result_out = xls_format_preference_zero_padded_hex;
   } else {
     absl::Status error = absl::InvalidArgumentError(absl::StrFormat(
         "Invalid value for conversion to XLS format preference: `%s`", s));
diff --git a/xls/public/c_api_format_preference.h b/xls/public/c_api_format_preference.h
index 783766b643..13b9581043 100644
--- a/xls/public/c_api_format_preference.h
+++ b/xls/public/c_api_format_preference.h
@@ -30,6 +30,8 @@ enum {
   xls_format_preference_hex,
   xls_format_preference_plain_binary,
   xls_format_preference_plain_hex,
+  xls_format_preference_zero_padded_binary,
+  xls_format_preference_zero_padded_hex,
 };
 
 }  // extern "C"
diff --git a/xls/public/c_api_impl_helpers.cc b/xls/public/c_api_impl_helpers.cc
index bb3875cdfe..581ddb70a2 100644
--- a/xls/public/c_api_impl_helpers.cc
+++ b/xls/public/c_api_impl_helpers.cc
@@ -84,6 +84,12 @@ bool FormatPreferenceFromC(xls_format_preference c_pref,
     case xls_format_preference_plain_hex:
       *cpp_pref = xls::FormatPreference::kPlainHex;
       break;
+    case xls_format_preference_zero_padded_binary:
+      *cpp_pref = xls::FormatPreference::kZeroPaddedBinary;
+      break;
+    case xls_format_preference_zero_padded_hex:
+      *cpp_pref = xls::FormatPreference::kZeroPaddedHex;
+      break;
     default:
       *error_out = ToOwnedCString(
           absl::StrFormat("Invalid format preference value: %d", c_pref));