diff --git a/Outputs/CRT/CRT.cpp b/Outputs/CRT/CRT.cpp
index 2a129284a..6d2f17f4a 100644
--- a/Outputs/CRT/CRT.cpp
+++ b/Outputs/CRT/CRT.cpp
@@ -406,6 +406,10 @@ void CRT::set_immediate_default_phase(float phase) {
 }
 
 void CRT::output_data(int number_of_cycles, size_t number_of_samples) {
+#ifndef NDEBUG
+	assert(number_of_samples > 0 && number_of_samples <= allocated_data_length_);
+	allocated_data_length_ = std::numeric_limits<size_t>::min();
+#endif
 	scan_target_->end_data(number_of_samples);
 	Scan scan;
 	scan.type = Scan::Type::Data;
diff --git a/Outputs/CRT/CRT.hpp b/Outputs/CRT/CRT.hpp
index 042521cc8..1982e378b 100644
--- a/Outputs/CRT/CRT.hpp
+++ b/Outputs/CRT/CRT.hpp
@@ -10,6 +10,7 @@
 #define CRT_hpp
 
 #include <cstdint>
+#include <limits>
 #include <memory>
 
 #include "../ScanTarget.hpp"
@@ -83,6 +84,10 @@ class CRT {
 		Outputs::Display::ScanTarget::Modals scan_target_modals_;
 		static const uint8_t DefaultAmplitude = 80;
 
+#ifndef NDEBUG
+		size_t allocated_data_length_ = std::numeric_limits<size_t>::min();
+#endif
+
 	public:
 		/*!	Constructs the CRT with a specified clock rate, height and colour subcarrier frequency.
 			The requested number of buffers, each with the requested number of bytes per pixel,
@@ -221,6 +226,9 @@ class CRT {
 			@returns A pointer to the allocated area if room is available; @c nullptr otherwise.
 		*/
 		inline uint8_t *begin_data(std::size_t required_length, std::size_t required_alignment = 1) {
+#ifndef NDEBUG
+			allocated_data_length_ = required_length;
+#endif
 			return scan_target_->begin_data(required_length, required_alignment);
 		}