diff --git a/exporters/otlp/src/otlp_http_client.cc b/exporters/otlp/src/otlp_http_client.cc
index e20236877f..2864af46a0 100644
--- a/exporters/otlp/src/otlp_http_client.cc
+++ b/exporters/otlp/src/otlp_http_client.cc
@@ -28,7 +28,7 @@ namespace google
 {
 namespace protobuf
 {
-LIBPROTOBUF_EXPORT int Base64Escape(const unsigned char *src, int slen, char *dest, int szdest);
+LIBPROTOBUF_EXPORT void Base64Escape(StringPiece src, std::string *dest);
 }  // namespace protobuf
 }  // namespace google
 #endif