diff --git a/system/HTTP/ContentSecurityPolicy.php b/system/HTTP/ContentSecurityPolicy.php
index dfea52a62772..e2a6bafa43c0 100644
--- a/system/HTTP/ContentSecurityPolicy.php
+++ b/system/HTTP/ContentSecurityPolicy.php
@@ -524,13 +524,32 @@ public function addConnectSrc($uri, ?bool $explicitReporting = null)
      *
      * @return $this
      */
-    public function setDefaultSrc($uri, ?bool $explicitReporting = null)
+    public function addDefaultSrc($uri, ?bool $explicitReporting = null)
     {
-        $this->defaultSrc = [(string) $uri => $explicitReporting ?? $this->reportOnly];
+        $this->addOption($uri, 'defaultSrc', $explicitReporting ?? $this->reportOnly);
 
         return $this;
     }
 
+    /**
+     * Sets the `default-src` directive, replacing any existing sources.
+     *
+     * `default-src` is the URI that is used for many of the settings when
+     * no other source has been set.
+     *
+     * @see http://www.w3.org/TR/CSP/#directive-default-src
+     *
+     * @param list<string>|string $uri
+     *
+     * @return $this
+     */
+    public function setDefaultSrc($uri, ?bool $explicitReporting = null)
+    {
+        $this->defaultSrc = [];
+
+        return $this->addDefaultSrc($uri, $explicitReporting);
+    }
+
     /**
      * Adds a new value to the `font-src` directive.
      *
diff --git a/tests/system/HTTP/ContentSecurityPolicyTest.php b/tests/system/HTTP/ContentSecurityPolicyTest.php
index 780cb99f31ea..a85cd107e7c3 100644
--- a/tests/system/HTTP/ContentSecurityPolicyTest.php
+++ b/tests/system/HTTP/ContentSecurityPolicyTest.php
@@ -617,6 +617,50 @@ public function testDefaultSrc(): void
         $this->assertContains('default-src iffy.com', $this->getCspDirectives($header));
     }
 
+    #[PreserveGlobalState(false)]
+    #[RunInSeparateProcess]
+    public function testDefaultSrcRich(): void
+    {
+        $this->csp->reportOnly(false);
+        $this->csp->setDefaultSrc(['self', 'maybe.com', 'iffy.com']);
+        $this->assertTrue($this->work());
+
+        $header = $this->getHeaderEmitted('Content-Security-Policy');
+        $this->assertIsString($header);
+        $this->assertContains("default-src 'self' maybe.com iffy.com", $this->getCspDirectives($header));
+    }
+
+    #[PreserveGlobalState(false)]
+    #[RunInSeparateProcess]
+    public function testAddDefaultSrc(): void
+    {
+        $this->csp->addDefaultSrc('maybe.com');
+        $this->csp->addDefaultSrc('iffy.com', true);
+        $this->assertTrue($this->work());
+
+        $header = $this->getHeaderEmitted('Content-Security-Policy-Report-Only');
+        $this->assertIsString($header);
+        $this->assertContains('default-src iffy.com', $this->getCspDirectives($header));
+
+        $header = $this->getHeaderEmitted('Content-Security-Policy');
+        $this->assertIsString($header);
+        $this->assertContains('default-src maybe.com', $this->getCspDirectives($header));
+    }
+
+    #[PreserveGlobalState(false)]
+    #[RunInSeparateProcess]
+    public function testAddDefaultSrcAppends(): void
+    {
+        $this->csp->reportOnly(false);
+        $this->csp->setDefaultSrc('maybe.com');
+        $this->csp->addDefaultSrc('iffy.com');
+        $this->assertTrue($this->work());
+
+        $header = $this->getHeaderEmitted('Content-Security-Policy');
+        $this->assertIsString($header);
+        $this->assertContains('default-src maybe.com iffy.com', $this->getCspDirectives($header));
+    }
+
     #[PreserveGlobalState(false)]
     #[RunInSeparateProcess]
     public function testReportURI(): void
diff --git a/user_guide_src/source/changelogs/v4.7.6.rst b/user_guide_src/source/changelogs/v4.7.6.rst
index 8739e9546d4c..e210d7897c06 100644
--- a/user_guide_src/source/changelogs/v4.7.6.rst
+++ b/user_guide_src/source/changelogs/v4.7.6.rst
@@ -38,6 +38,7 @@ Bugs Fixed
   is used instead. Values that cannot be converted to a string, such as objects
   not implementing ``Stringable``, now throw a ``FormatException`` instead of a
   fatal ``Error``.
+- **HTTP:** Fixed a bug in ``ContentSecurityPolicy::setDefaultSrc()`` where passing an array of URIs resulted in an invalid ``'Array'`` directive. Added ``ContentSecurityPolicy::addDefaultSrc()`` to allow appending sources to the ``default-src`` directive.
 - **Security:** Fixed a bug where a valid JSON request body that is not an object
   (for example a JSON array) was corrupted after CSRF verification when the
   token was sent via the ``X-CSRF-TOKEN`` header.