diff --git a/CMakeLists.txt b/CMakeLists.txt
index 72bf5a95..3e50f0b5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -305,6 +305,10 @@ if(GENERATE_AUTO_JOB)
   add_custom_target(auto_job_files ALL DEPENDS ${auto_job_outputs})
 endif()
 
+add_test(
+  NAME check-assert
+  COMMAND perl ${qpdf_SOURCE_DIR}/check_assert)
+
 # add_subdirectory order affects test order
 add_subdirectory(include)
 add_subdirectory(libqpdf)
diff --git a/README-maintainer b/README-maintainer
index 2e11a11b..88e81461 100644
--- a/README-maintainer
+++ b/README-maintainer
@@ -123,11 +123,23 @@ CODING RULES
   "Code Formatting" section in manual/contributing.rst for details.
   See also "CODE FORMATTING" below.
 
-* Do not use assert in non-test code for any purpose other than as a
-  sanity check during development that would be safe to remove in
-  production. assert is for strong invariant checking. When developing
-  and using assert for that purpose, make sure to use the Debug
-  configuration since assert is disabled in other configurations.
+* Use of assert:
+
+  * Test code: #include <qpdf/assert_test.h> first.
+  * Debug code: #include <qpdf/assert_debug.h> first and use
+    qpdf_assert_debug instead of assert.
+
+  These rules are enforced by the check-assert test. This practices
+  serves to
+
+  * remind us that assert in release code disappears and so should only
+    be used for debugging; when doing so use a Debug build
+    configuration
+
+  * protect us from using assert in test code without explicitly
+    removing the NDEBUG definition, since that would cause the assert
+    not to actually be testing anything in non-Debug build
+    configurations.
 
 * In a source file, include the header file that declares the source
   class first followed by a blank line. If a config file is needed
diff --git a/check_assert b/check_assert
new file mode 100755
index 00000000..81ecf788
--- /dev/null
+++ b/check_assert
@@ -0,0 +1,62 @@
+#!/usr/bin/env perl
+require 5.008;
+use warnings;
+use strict;
+use File::Basename;
+
+my $whoami = basename($0);
+chdir(dirname($0)) or die;
+
+my $errors = 0;
+foreach my $file (glob('*/*.c'), glob('*/*.cc'),
+                  glob('*/*/*.h'), glob('*/*/*.hh'))
+{
+    my $assert_test = 0;
+    if ($file =~ m,^libqpdf/qpdf/assert_,)
+    {
+        next;
+    }
+    open(F, "<$file") or die;
+    my $first_include = undef;
+    while (<F>)
+    {
+        if (m,^\s*#\s*include <qpdf/assert_(.*?).h>,)
+        {
+            if ($1 eq 'test')
+            {
+                $assert_test = 1;
+            }
+            if (defined $first_include)
+            {
+                error("$file:$.: qpdf/assert header must be first");
+            }
+        }
+        if (m,^\s*#\s*include <(.*?)>,)
+        {
+            my $header = $1;
+            if (($header eq 'cassert') || ($header eq 'assert.h'))
+            {
+                error("$file:$.: assert.h and cassert are not allowed --" .
+                      " use one of the qpdf/assert_ files instead");
+            }
+            $first_include = 1;
+        }
+        if ((! $assert_test) && (m/assert\(/))
+        {
+            error("$file:$.: call qpdf_assert_debug instead of assert");
+        }
+    }
+    close(F);
+}
+if ($errors)
+{
+    die "$whoami: errors detected\n";
+}
+print "$whoami: no incorrect use of assert found\n";
+
+sub error
+{
+    my $msg = shift;
+    warn $msg, "\n";
+    $errors = 1;
+}
diff --git a/include/qpdf/QIntC.hh b/include/qpdf/QIntC.hh
index ce2f47e9..dadc7582 100644
--- a/include/qpdf/QIntC.hh
+++ b/include/qpdf/QIntC.hh
@@ -24,7 +24,6 @@
 
 #include <qpdf/DLL.h>
 #include <qpdf/Types.h>
-#include <cassert>
 #include <iostream>
 #include <limits>
 #include <locale>
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index e5270449..103abee1 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -1,4 +1,6 @@
-#include <qpdf/qpdf-config.h> // include first for large file support
+#include <qpdf/assert_debug.h>
+
+#include <qpdf/qpdf-config.h> // include early for large file support
 
 #include <qpdf/QPDFWriter.hh>
 
@@ -21,7 +23,6 @@
 #include <qpdf/RC4.hh>
 
 #include <algorithm>
-#include <cassert>
 #include <stdlib.h>
 
 QPDFWriter::Members::Members(QPDF& pdf) :
@@ -996,7 +997,7 @@ QPDFWriter::writePad(int nspaces)
 Pipeline*
 QPDFWriter::pushPipeline(Pipeline* p)
 {
-    assert(dynamic_cast<Pl_Count*>(p) == 0);
+    qpdf_assert_debug(dynamic_cast<Pl_Count*>(p) == 0);
     this->m->pipeline_stack.push_back(p);
     return p;
 }
@@ -1027,9 +1028,9 @@ QPDFWriter::PipelinePopper::~PipelinePopper()
     if (stack_id.empty()) {
         return;
     }
-    assert(qw->m->pipeline_stack.size() >= 2);
+    qpdf_assert_debug(qw->m->pipeline_stack.size() >= 2);
     qw->m->pipeline->finish();
-    assert(
+    qpdf_assert_debug(
         dynamic_cast<Pl_Count*>(qw->m->pipeline_stack.back()) ==
         qw->m->pipeline);
     // It might be possible for this assertion to fail if
@@ -1038,7 +1039,7 @@ QPDFWriter::PipelinePopper::~PipelinePopper()
     // which two dynamically allocated PipelinePopper objects ever
     // exist at the same time, so the assertion will fail if they get
     // popped out of order from automatic destruction.
-    assert(qw->m->pipeline->getIdentifier() == stack_id);
+    qpdf_assert_debug(qw->m->pipeline->getIdentifier() == stack_id);
     delete qw->m->pipeline_stack.back();
     qw->m->pipeline_stack.pop_back();
     while (dynamic_cast<Pl_Count*>(qw->m->pipeline_stack.back()) == 0) {
@@ -1109,9 +1110,9 @@ QPDFWriter::pushMD5Pipeline(PipelinePopper& pp)
         throw std::logic_error("Deterministic ID computation enabled after ID"
                                " generation has already occurred.");
     }
-    assert(this->m->deterministic_id);
-    assert(this->m->md5_pipeline == 0);
-    assert(this->m->pipeline->getCount() == 0);
+    qpdf_assert_debug(this->m->deterministic_id);
+    qpdf_assert_debug(this->m->md5_pipeline == 0);
+    qpdf_assert_debug(this->m->pipeline->getCount() == 0);
     this->m->md5_pipeline = new Pl_MD5("qpdf md5", this->m->pipeline);
     this->m->md5_pipeline->persistAcrossFinish(true);
     // Special case code in popPipelineStack clears this->m->md5_pipeline
@@ -1123,8 +1124,8 @@ QPDFWriter::pushMD5Pipeline(PipelinePopper& pp)
 void
 QPDFWriter::computeDeterministicIDData()
 {
-    assert(this->m->md5_pipeline != 0);
-    assert(this->m->deterministic_id_data.empty());
+    qpdf_assert_debug(this->m->md5_pipeline != 0);
+    qpdf_assert_debug(this->m->deterministic_id_data.empty());
     this->m->deterministic_id_data = this->m->md5_pipeline->getHexDigest();
     this->m->md5_pipeline->enable(false);
 }
@@ -1786,7 +1787,7 @@ QPDFWriter::writeObjectStream(QPDFObjectHandle object)
     // object stream that we are generating from scratch.
 
     QPDFObjGen old_og = object.getObjGen();
-    assert(old_og.getGen() == 0);
+    qpdf_assert_debug(old_og.getGen() == 0);
     int old_id = old_og.getObj();
     int new_id = this->m->obj_renumber[old_og];
 
@@ -3003,7 +3004,7 @@ QPDFWriter::writeLinearized()
         closeObject(lindict_id);
         static int const pad = 200;
         int spaces = QIntC::to_int(pos - this->m->pipeline->getCount() + pad);
-        assert(spaces >= 0);
+        qpdf_assert_debug(spaces >= 0);
         writePad(spaces);
         writeString("\n");
 
@@ -3177,7 +3178,7 @@ QPDFWriter::writeLinearized()
                     need_xref_stream ? 0 : 1);
                 computeDeterministicIDData();
                 pp_md5 = 0;
-                assert(this->m->md5_pipeline == 0);
+                qpdf_assert_debug(this->m->md5_pipeline == 0);
             }
 
             // Close first pass pipeline
@@ -3377,6 +3378,6 @@ QPDFWriter::writeStandard()
             "QPDFWriter standard deterministic ID",
             this->m->object_stream_to_objects.empty() ? 0 : 1);
         pp_md5 = 0;
-        assert(this->m->md5_pipeline == 0);
+        qpdf_assert_debug(this->m->md5_pipeline == 0);
     }
 }
diff --git a/libqpdf/QPDF_encryption.cc b/libqpdf/QPDF_encryption.cc
index 14b22d88..6a9ad871 100644
--- a/libqpdf/QPDF_encryption.cc
+++ b/libqpdf/QPDF_encryption.cc
@@ -1,6 +1,8 @@
 // This file implements methods from the QPDF class that involve
 // encryption.
 
+#include <qpdf/assert_debug.h>
+
 #include <qpdf/QPDF.hh>
 
 #include <qpdf/QPDFExc.hh>
@@ -15,7 +17,6 @@
 #include <qpdf/RC4.hh>
 
 #include <algorithm>
-#include <cassert>
 #include <string.h>
 
 static unsigned char const padding_string[] = {
@@ -288,7 +289,7 @@ hash_V5(
 
             ++round_number;
             std::string K1 = password + K + udata;
-            assert(K.length() >= 32);
+            qpdf_assert_debug(K.length() >= 32);
             std::string E = process_with_aes(
                 K.substr(0, 16),
                 true,
diff --git a/libqpdf/QPDF_optimization.cc b/libqpdf/QPDF_optimization.cc
index ac1bbfe6..4204a20d 100644
--- a/libqpdf/QPDF_optimization.cc
+++ b/libqpdf/QPDF_optimization.cc
@@ -1,12 +1,13 @@
 // See the "Optimization" section of the manual.
 
+#include <qpdf/assert_debug.h>
+
 #include <qpdf/QPDF.hh>
 
 #include <qpdf/QPDFExc.hh>
 #include <qpdf/QPDF_Array.hh>
 #include <qpdf/QPDF_Dictionary.hh>
 #include <qpdf/QTC.hh>
-#include <cassert>
 
 QPDF::ObjUser::ObjUser() :
     ou_type(ou_bad),
@@ -18,14 +19,14 @@ QPDF::ObjUser::ObjUser(user_e type) :
     ou_type(type),
     pageno(0)
 {
-    assert(type == ou_root);
+    qpdf_assert_debug(type == ou_root);
 }
 
 QPDF::ObjUser::ObjUser(user_e type, int pageno) :
     ou_type(type),
     pageno(pageno)
 {
-    assert((type == ou_page) || (type == ou_thumb));
+    qpdf_assert_debug((type == ou_page) || (type == ou_thumb));
 }
 
 QPDF::ObjUser::ObjUser(user_e type, std::string const& key) :
@@ -33,7 +34,7 @@ QPDF::ObjUser::ObjUser(user_e type, std::string const& key) :
     pageno(0),
     key(key)
 {
-    assert((type == ou_trailer_key) || (type == ou_root_key));
+    qpdf_assert_debug((type == ou_trailer_key) || (type == ou_root_key));
 }
 
 bool
diff --git a/libqpdf/qpdf/assert_debug.h b/libqpdf/qpdf/assert_debug.h
new file mode 100644
index 00000000..0543d8fb
--- /dev/null
+++ b/libqpdf/qpdf/assert_debug.h
@@ -0,0 +1,18 @@
+/*
+ * Include this file to use assert in regular code for
+ * debugging/strong sanity checking, knowing that the assert will be
+ * disabled in release code. Use qpdf_assert_debug in the code.
+ */
+
+/* assert_debug and assert_test intentionally use the same
+ * guard. Search for assert in README-MAINTAINER.
+ */
+#ifdef QPDF_ASSERT_H
+# error "At most one qpdf/assert header may be included at most one time"
+#else
+# define QPDF_ASSERT_H
+
+# include <assert.h>
+# define qpdf_assert_debug assert
+
+#endif /* QPDF_ASSERT_H */
diff --git a/libqpdf/qpdf/assert_test.h b/libqpdf/qpdf/assert_test.h
new file mode 100644
index 00000000..5310cdaa
--- /dev/null
+++ b/libqpdf/qpdf/assert_test.h
@@ -0,0 +1,20 @@
+/*
+ * Include this file to use assert in regular code for
+ * debugging/strong sanity checking, knowing that the assert will be
+ * disabled in release code. Use qpdf_debug_assert in the code.
+ */
+
+/* assert_debug and assert_test intentionally use the same
+ * guard. Search for assert in README-MAINTAINER.
+ */
+#ifdef QPDF_ASSERT_H
+# error "At most one qpdf/assert header may be included at most one time"
+#else
+# define QPDF_ASSERT_H
+
+# ifdef NDEBUG
+#  undef NDEBUG
+# endif
+# include <assert.h>
+
+#endif /* QPDF_ASSERT_H */
diff --git a/libtests/arg_parser.cc b/libtests/arg_parser.cc
index 8b4d556a..1480a717 100644
--- a/libtests/arg_parser.cc
+++ b/libtests/arg_parser.cc
@@ -1,15 +1,11 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/QPDFArgParser.hh>
 #include <qpdf/QPDFUsage.hh>
 #include <qpdf/QUtil.hh>
 #include <cstring>
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 class ArgParser
 {
   public:
diff --git a/libtests/base64.cc b/libtests/base64.cc
index 66f2d828..0ce6f9a3 100644
--- a/libtests/base64.cc
+++ b/libtests/base64.cc
@@ -1,8 +1,9 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/Pl_Base64.hh>
 
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/QUtil.hh>
-#include <cassert>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
diff --git a/libtests/buffer.cc b/libtests/buffer.cc
index a24c0f99..a65efb1c 100644
--- a/libtests/buffer.cc
+++ b/libtests/buffer.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/Pl_Buffer.hh>
 #include <qpdf/Pl_Count.hh>
 #include <qpdf/Pl_Discard.hh>
@@ -7,12 +9,6 @@
 #include <stdexcept>
 #include <stdlib.h>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static unsigned char*
 uc(char const* s)
 {
diff --git a/libtests/concatenate.cc b/libtests/concatenate.cc
index 10902adf..9bc0fd04 100644
--- a/libtests/concatenate.cc
+++ b/libtests/concatenate.cc
@@ -1,15 +1,11 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/Pl_Buffer.hh>
 #include <qpdf/Pl_Concatenate.hh>
 #include <qpdf/Pl_Flate.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static void
 pipeStringAndFinish(Pipeline* p, std::string const& str)
 {
diff --git a/libtests/cxx11.cc b/libtests/cxx11.cc
index 4c2c2cb6..250e7e2b 100644
--- a/libtests/cxx11.cc
+++ b/libtests/cxx11.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
@@ -9,12 +11,6 @@
 #include <type_traits>
 #include <vector>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 // Functional programming
 
 // Function that returns a callable in the form of a lambda
diff --git a/libtests/json.cc b/libtests/json.cc
index 43f2b3c6..3844222f 100644
--- a/libtests/json.cc
+++ b/libtests/json.cc
@@ -1,13 +1,9 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/JSON.hh>
 #include <qpdf/QPDFObjectHandle.hh>
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static void
 check(JSON const& j, std::string const& exp)
 {
diff --git a/libtests/json_handler.cc b/libtests/json_handler.cc
index 567cde86..4e610b08 100644
--- a/libtests/json_handler.cc
+++ b/libtests/json_handler.cc
@@ -1,14 +1,10 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/JSONHandler.hh>
 #include <qpdf/QPDFUsage.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static void
 print_null(std::string const& path)
 {
diff --git a/libtests/matrix.cc b/libtests/matrix.cc
index 7dc73390..f69d270c 100644
--- a/libtests/matrix.cc
+++ b/libtests/matrix.cc
@@ -1,13 +1,9 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/QPDFMatrix.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static void
 check(QPDFMatrix const& m, std::string const& exp)
 {
diff --git a/libtests/pdf_version.cc b/libtests/pdf_version.cc
index e9bfb00b..5db444b3 100644
--- a/libtests/pdf_version.cc
+++ b/libtests/pdf_version.cc
@@ -1,13 +1,9 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/PDFVersion.hh>
 
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 int
 main()
 {
diff --git a/libtests/predictors.cc b/libtests/predictors.cc
index c024cbd6..a8f6c5d9 100644
--- a/libtests/predictors.cc
+++ b/libtests/predictors.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/Pl_PNGFilter.hh>
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/Pl_TIFFPredictor.hh>
@@ -9,12 +11,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 void
 run(char const* filename,
     char const* filter,
diff --git a/libtests/qintc.cc b/libtests/qintc.cc
index d3e19f5b..d5738a4b 100644
--- a/libtests/qintc.cc
+++ b/libtests/qintc.cc
@@ -1,12 +1,8 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/QIntC.hh>
 #include <stdint.h>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 #define try_convert(exp_pass, fn, i) \
  try_convert_real(#fn "(" #i ")", exp_pass, fn, i)
 
diff --git a/libtests/qutil.cc b/libtests/qutil.cc
index 017f371b..f79f9a3f 100644
--- a/libtests/qutil.cc
+++ b/libtests/qutil.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/Pl_Buffer.hh>
 #include <qpdf/QPDFSystemError.hh>
 #include <qpdf/QUtil.hh>
@@ -17,12 +19,6 @@
 # include <unistd.h>
 #endif
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 template <class int_T>
 void
 test_to_number(
diff --git a/libtests/rc4.cc b/libtests/rc4.cc
index 7245ef86..1b1a8744 100644
--- a/libtests/rc4.cc
+++ b/libtests/rc4.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/Pl_RC4.hh>
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/QIntC.hh>
@@ -8,12 +10,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static void
 other_tests()
 {
diff --git a/libtests/sparse_array.cc b/libtests/sparse_array.cc
index 8d37bc2f..62410399 100644
--- a/libtests/sparse_array.cc
+++ b/libtests/sparse_array.cc
@@ -1,12 +1,8 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/SparseOHArray.hh>
 #include <iostream>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 int
 main()
 {
diff --git a/qpdf/CMakeLists.txt b/qpdf/CMakeLists.txt
index 94cf9e2d..bc4ddf11 100644
--- a/qpdf/CMakeLists.txt
+++ b/qpdf/CMakeLists.txt
@@ -29,6 +29,16 @@ endforeach()
 target_include_directories(qpdf-ctest PRIVATE ${CMAKE_BINARY_DIR}/libqpdf)
 target_include_directories(sizes PRIVATE ${JPEG_INCLUDE})
 
+set(needs_private_headers
+  test_large_file
+  test_driver
+  qpdf-ctest
+  qpdfjob-ctest
+  )
+foreach(TARGET ${needs_private_headers})
+  target_include_directories(${TARGET} PRIVATE ${CMAKE_SOURCE_DIR}/libqpdf)
+endforeach()
+
 foreach(B qpdf test_unicode_filenames fix-qdf test_shell_glob)
   if(WINDOWS_WMAIN_COMPILE)
     target_compile_options(${B} PRIVATE ${WINDOWS_WMAIN_COMPILE})
diff --git a/qpdf/qpdf-ctest.c b/qpdf/qpdf-ctest.c
index 62274c52..07d6ca9e 100644
--- a/qpdf/qpdf-ctest.c
+++ b/qpdf/qpdf-ctest.c
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/qpdf-c.h>
 #include <errno.h>
 #include <stdio.h>
@@ -6,12 +8,6 @@
 
 #include <qpdf/qpdf-config.h> // for LL_FMT -- special case in build
 
-#ifdef NDEBUG
-/* We need assert even in a release build for test code. */
-# undef NDEBUG
-#endif
-#include <assert.h>
-
 static char* whoami = 0;
 static qpdf_data qpdf = 0;
 
diff --git a/qpdf/qpdfjob-ctest.c b/qpdf/qpdfjob-ctest.c
index e67890e8..8d5e374e 100644
--- a/qpdf/qpdfjob-ctest.c
+++ b/qpdf/qpdfjob-ctest.c
@@ -1,14 +1,10 @@
+#include <qpdf/assert_test.h>
+
 #include <qpdf/qpdfjob-c.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef NDEBUG
-/* We need assert even in a release build for test code. */
-# undef NDEBUG
-#endif
-#include <assert.h>
-
 #ifndef QPDF_NO_WCHAR_T
 static void
 wide_test()
diff --git a/qpdf/test_driver.cc b/qpdf/test_driver.cc
index f0c56176..1934b02b 100644
--- a/qpdf/test_driver.cc
+++ b/qpdf/test_driver.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 // This program tests miscellaneous functionality in the qpdf library
 // that we don't want to pollute the qpdf program with.
 
@@ -32,12 +34,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 static char const* whoami = 0;
 
 void
diff --git a/qpdf/test_large_file.cc b/qpdf/test_large_file.cc
index 32494426..904f3dd6 100644
--- a/qpdf/test_large_file.cc
+++ b/qpdf/test_large_file.cc
@@ -1,3 +1,5 @@
+#include <qpdf/assert_test.h>
+
 // NOTE: This test program doesn't do anything special to enable large
 // file support.  This is important since it verifies that programs
 // don't have to do anything special -- all the work is done
@@ -14,12 +16,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef NDEBUG
-// We need assert even in a release build for test code.
-# undef NDEBUG
-#endif
-#include <cassert>
-
 // Run "test_large_file write small a.pdf" to get a PDF file that you
 // can look at in a reader.