diff --git a/src/Replace/NamespaceReplacer.php b/src/Replace/NamespaceReplacer.php
index 711ec086..022cea11 100644
--- a/src/Replace/NamespaceReplacer.php
+++ b/src/Replace/NamespaceReplacer.php
@@ -29,11 +29,15 @@ public function replace($contents, $file = null)
                 (                            # Start the namespace matcher
                   (?<!$dependencyNamespace)  # Does NOT start with the prefix
                   (?<![a-zA-Z0-9_]\\\\)      # Not a class-allowed character followed by a slash
-                  (?<!class\s)				 # Not a class declaration.
-                  $searchNamespace           # The namespace we're looking for
-                  [\\\|;\s]                  # Backslash, pipe, semicolon, or space
+                  (?<!class\s)				 # Not a class declaration
+                  $searchNamespace			 # The namespace were looking for
+                  (?=;|\\\|\||\sas)			 # Followed by one of
+                  							 # semicolon when it is the class namespace itself
+                  				             # backslash when it is part of a longer namespace or namespaced class
+                  							 # pipe
+                  							 # space followed by the as keyword
                 )                            # End the namespace matcher
-            /Ux",
+            /Ux", # U non-greedy matching by default, x ignore whitespace in regex.
             function ($matches) {
                 return $matches[1] . $this->dep_namespace . $matches[2];
             },
diff --git a/tests/replacers/NamespaceReplacerIntegrationTest.php b/tests/replacers/NamespaceReplacerIntegrationTest.php
index 80bc04a3..c2e7094f 100644
--- a/tests/replacers/NamespaceReplacerIntegrationTest.php
+++ b/tests/replacers/NamespaceReplacerIntegrationTest.php
@@ -103,6 +103,47 @@ public function test_it_does_not_make_classname_replacement_inside_namespaced_fi
     }
 
 
+
+    /**
+     * Another Mpdf problem, presumably down to the classname matching the namespace.
+     *
+     * Typed function properties whose class type (name) match the namespace being replaced are
+     * unintentionally prefixed, causing PHP to crash.
+     *
+     * Occurring at dev-master#3b1243ca8505fa6436569800dc34269178930f39
+     *
+     * @see https://github.com/coenjacobs/mozart/issues/124
+     */
+    public function test_it_does_not_prefix_function_argument_types_whose_classname_matches_the_namespace()
+    {
+
+        $composer = $this->composer;
+
+        $composer->require["mpdf/mpdf"] = "8.0.10";
+
+        file_put_contents($this->testsWorkingDir . '/composer.json', json_encode($composer));
+
+        chdir($this->testsWorkingDir);
+
+        exec('composer update');
+
+        $inputInterfaceMock = $this->createMock(InputInterface::class);
+        $outputInterfaceMock = $this->createMock(OutputInterface::class);
+
+        $mozartCompose = new Compose();
+
+        $mozartCompose->run($inputInterfaceMock, $outputInterfaceMock);
+
+        $mpdf_php = file_get_contents($this->testsWorkingDir .'/dep_directory/Mpdf/Conversion/DecToOther.php');
+
+        // Confirm problem is gone.
+        $this->assertStringNotContainsString('public function __construct(Mozart\Mpdf $mpdf)', $mpdf_php);
+
+        // Confirm solution is correct.
+        $this->assertStringContainsString('public function __construct(Mpdf $mpdf)', $mpdf_php);
+    }
+
+
     /**
      * Delete $this->testsWorkingDir after each test.
      *
diff --git a/tests/replacers/NamespaceReplacerTest.php b/tests/replacers/NamespaceReplacerTest.php
index d317378a..d5f89da0 100644
--- a/tests/replacers/NamespaceReplacerTest.php
+++ b/tests/replacers/NamespaceReplacerTest.php
@@ -123,4 +123,20 @@ public function it_replaces_namespace_use_as_declarations(): void
 
         $this->assertEquals($expected, $replacer->replace($contents));
     }
+
+/**
+ * @test
+ */
+public function it_doesnt_prefix_function_types_that_happen_to_match_the_namespace() {
+
+    $namespace = 'Mpdf';
+    $prefix = "Mozart\\";
+
+    $replacer = self::createReplacer($namespace, $prefix);
+
+    $contents = 'public function getServices( Mpdf $mpdf, LoggerInterface $logger, $config, )';
+    $expected = 'public function getServices( Mpdf $mpdf, LoggerInterface $logger, $config, )';
+
+    $this->assertEquals($expected, $replacer->replace($contents));
+}
 }