diff --git a/libqpdf/Pl_Buffer.cc b/libqpdf/Pl_Buffer.cc
index 9994bedd..1babe6e1 100644
--- a/libqpdf/Pl_Buffer.cc
+++ b/libqpdf/Pl_Buffer.cc
@@ -19,6 +19,9 @@ Pl_Buffer::~Pl_Buffer() // NOLINT (modernize-use-equals-default)
 void
 Pl_Buffer::write(unsigned char const* buf, size_t len)
 {
+    if (!len) {
+        return;
+    }
     m->data.append(reinterpret_cast<char const*>(buf), len);
     m->ready = false;
 
diff --git a/libqpdf/Pl_String.cc b/libqpdf/Pl_String.cc
index 9009268a..1369c17d 100644
--- a/libqpdf/Pl_String.cc
+++ b/libqpdf/Pl_String.cc
@@ -21,6 +21,9 @@ Pl_String::~Pl_String() // NOLINT (modernize-use-equals-default)
 void
 Pl_String::write(unsigned char const* buf, size_t len)
 {
+    if (!len) {
+        return;
+    }
     m->s.append(reinterpret_cast<char const*>(buf), len);
     if (getNext(true)) {
         getNext()->write(buf, len);