diff --git a/fuzz/CMakeLists.txt b/fuzz/CMakeLists.txt
index daacf030..6b3cccf8 100644
--- a/fuzz/CMakeLists.txt
+++ b/fuzz/CMakeLists.txt
@@ -149,6 +149,7 @@ set(CORPUS_OTHER
   99999e.fuzz
   369662293.fuzz
   369662293a.fuzz
+  377977949.fuzz
 )
 
 set(CORPUS_DIR ${CMAKE_CURRENT_BINARY_DIR}/qpdf_corpus)
diff --git a/fuzz/qpdf_extra/377977949.fuzz b/fuzz/qpdf_extra/377977949.fuzz
new file mode 100644
index 00000000..bb355984
Binary files /dev/null and b/fuzz/qpdf_extra/377977949.fuzz differ
diff --git a/fuzz/qtest/fuzz.test b/fuzz/qtest/fuzz.test
index 6448d5f0..efffdc67 100644
--- a/fuzz/qtest/fuzz.test
+++ b/fuzz/qtest/fuzz.test
@@ -11,7 +11,7 @@ my $td = new TestDriver('fuzz');
 
 my $qpdf_corpus = $ENV{'QPDF_FUZZ_CORPUS'} || die "must set QPDF_FUZZ_CORPUS";
 
-my $n_qpdf_files = 86;       # increment when adding new files
+my $n_qpdf_files = 87;       # increment when adding new files
 
 my @fuzzers = (
     ['ascii85' => 1],
diff --git a/libqpdf/Pl_AES_PDF.cc b/libqpdf/Pl_AES_PDF.cc
index d621bdd8..8b3982ba 100644
--- a/libqpdf/Pl_AES_PDF.cc
+++ b/libqpdf/Pl_AES_PDF.cc
@@ -23,6 +23,9 @@ Pl_AES_PDF::Pl_AES_PDF(
     if (!next) {
         throw std::logic_error("Attempt to create Pl_AES_PDF with nullptr as next");
     }
+    if (!(key_bytes == 32 || key_bytes == 16)) {
+        throw std::runtime_error("unsupported key length");
+    }
     this->key = std::make_unique<unsigned char[]>(key_bytes);
     std::memcpy(this->key.get(), key, key_bytes);
     std::memset(this->inbuf, 0, this->buf_size);