diff --git a/include/qpdf/Pl_Buffer.hh b/include/qpdf/Pl_Buffer.hh
index 5030e10..6cf4560 100644
--- a/include/qpdf/Pl_Buffer.hh
+++ b/include/qpdf/Pl_Buffer.hh
@@ -33,7 +33,7 @@
 #include <qpdf/PointerHolder.hh> // unused -- remove in qpdf 12 (see #785)
 
 #include <memory>
-#include <vector>
+#include <string>
 
 class QPDF_DLL_CLASS Pl_Buffer: public Pipeline
 {
@@ -78,7 +78,7 @@ class QPDF_DLL_CLASS Pl_Buffer: public Pipeline
         Members(Members const&) = delete;
 
         bool ready{true};
-        std::vector<unsigned char> data;
+        std::string data;
     };
 
     std::shared_ptr<Members> m;
diff --git a/libqpdf/Pl_Buffer.cc b/libqpdf/Pl_Buffer.cc
index 766c04b..072b04d 100644
--- a/libqpdf/Pl_Buffer.cc
+++ b/libqpdf/Pl_Buffer.cc
@@ -19,7 +19,7 @@ Pl_Buffer::~Pl_Buffer() // NOLINT (modernize-use-equals-default)
 void
 Pl_Buffer::write(unsigned char const* buf, size_t len)
 {
-    m->data.insert(m->data.end(), buf, buf + len);
+    m->data.append(reinterpret_cast<char const*>(buf), len);
     m->ready = false;
 
     if (getNext(true)) {