diff --git a/include/libcamera/framebuffer.h b/include/libcamera/framebuffer.h
index 5de3c744..79541557 100644
--- a/include/libcamera/framebuffer.h
+++ b/include/libcamera/framebuffer.h
@@ -7,6 +7,8 @@
 #ifndef __LIBCAMERA_FRAMEBUFFER_H__
 #define __LIBCAMERA_FRAMEBUFFER_H__
 
+#include <assert.h>
+#include <limits>
 #include <stdint.h>
 #include <vector>
 
@@ -41,14 +43,21 @@ class FrameBuffer final : public Extensible
 
 public:
 	struct Plane {
+		static constexpr unsigned int kInvalidOffset = std::numeric_limits<unsigned int>::max();
 		FileDescriptor fd;
-		unsigned int offset;
+		unsigned int offset = kInvalidOffset;
 		unsigned int length;
 	};
 
 	FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie = 0);
 
-	const std::vector<Plane> &planes() const { return planes_; }
+	const std::vector<Plane> &planes() const
+	{
+		/* \todo remove this assert. */
+		for (const auto &plane : planes_)
+			assert(plane.offset != Plane::kInvalidOffset);
+		return planes_;
+	}
 
 	Request *request() const;
 	const FrameMetadata &metadata() const { return metadata_; }