diff --git a/ChangeLog b/ChangeLog
index ba03fe8..5fd1ce6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2024-02-01  M Holger  <m.holger@qpdf.org>
+
+	* Bug fix: in qpdf CLI / QPDFJob throw a QPDFUsage exception if a
+	parameter is given for a flag. Previously the parameter was ignored and
+	e.g. --encrypt=n was treated as --encrypt. Fixes #1329.
+
 2024-09-20  Chao Li  <mslichao@outlook.com>
 
 	* Add C API function qpdf_oh_free_buffer to release memory allocated
diff --git a/libqpdf/QPDFArgParser.cc b/libqpdf/QPDFArgParser.cc
index 5377b2b..fc8f2ef 100644
--- a/libqpdf/QPDFArgParser.cc
+++ b/libqpdf/QPDFArgParser.cc
@@ -9,6 +9,8 @@
 #include <cstring>
 #include <iostream>
 
+using namespace std::literals;
+
 QPDFArgParser::Members::Members(int argc, char const* const argv[], char const* progname_env) :
 
     argc(argc),
@@ -532,7 +534,13 @@ QPDFArgParser::parseArgs()
             }
             usage(message);
         }
+
         if (oe.bare_arg_handler) {
+            if (have_parameter) {
+                usage(
+                    "--"s + arg_s + " does not take a parameter, but \"" + parameter +
+                    "\" was given");
+            }
             oe.bare_arg_handler();
         } else if (oe.param_arg_handler) {
             oe.param_arg_handler(parameter);
diff --git a/qpdf/qtest/arg-parsing.test b/qpdf/qtest/arg-parsing.test
index 238f19c..395e469 100644
--- a/qpdf/qtest/arg-parsing.test
+++ b/qpdf/qtest/arg-parsing.test
@@ -15,7 +15,7 @@ cleanup();
 
 my $td = new TestDriver('arg-parsing');
 
-my $n_tests = 25;
+my $n_tests = 26;
 
 $td->runtest("required argument",
              {$td->COMMAND => "qpdf --password minimal.pdf"},
@@ -32,6 +32,11 @@ $td->runtest("required argument with choices",
              {$td->REGEXP => "must be given as --decode-level=\\{.*all.*\\}",
                   $td->EXIT_STATUS => 2},
              $td->NORMALIZE_NEWLINES);
+$td->runtest("flag with parameter",
+             {$td->COMMAND => "qpdf --qdf=false minimal.pdf"},
+             {$td->REGEXP => "--qdf does not take a parameter, but \"false\" was given",
+                  $td->EXIT_STATUS => 2},
+             $td->NORMALIZE_NEWLINES);
 copy("minimal.pdf", '@file.pdf');
 $td->runtest("\@file exists and file doesn't",
              {$td->COMMAND => "qpdf --check \@file.pdf"},