diff --git a/Libraries/LibWeb/HTML/ImageData.cpp b/Libraries/LibWeb/HTML/ImageData.cpp
index 160320abc85..39c07c8493d 100644
--- a/Libraries/LibWeb/HTML/ImageData.cpp
+++ b/Libraries/LibWeb/HTML/ImageData.cpp
@@ -143,12 +143,12 @@ void ImageData::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_data);
 }
 
-unsigned ImageData::width() const
+WebIDL::UnsignedLong ImageData::width() const
 {
     return m_bitmap->width();
 }
 
-unsigned ImageData::height() const
+WebIDL::UnsignedLong ImageData::height() const
 {
     return m_bitmap->height();
 }
diff --git a/Libraries/LibWeb/HTML/ImageData.h b/Libraries/LibWeb/HTML/ImageData.h
index 079f0b8d875..3fa6036e5bb 100644
--- a/Libraries/LibWeb/HTML/ImageData.h
+++ b/Libraries/LibWeb/HTML/ImageData.h
@@ -10,6 +10,7 @@
 #include <LibGfx/Forward.h>
 #include <LibWeb/Bindings/ImageDataPrototype.h>
 #include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/WebIDL/Types.h>
 
 namespace Web::HTML {
 
@@ -30,8 +31,8 @@ public:
 
     virtual ~ImageData() override;
 
-    unsigned width() const;
-    unsigned height() const;
+    WebIDL::UnsignedLong width() const;
+    WebIDL::UnsignedLong height() const;
 
     Gfx::Bitmap& bitmap() { return m_bitmap; }
     Gfx::Bitmap const& bitmap() const { return m_bitmap; }