Noir is a Domain Specific Language for SNARK proving systems that is designed to use any ACIR compatible proving system, and Brillig is the bytecode ACIR uses for non-determinism. Noir programs can invoke external functions through foreign calls. When compiling to Brillig bytecode, the SSA instructions are processed block-by-block in "BrilligBlock::compile_block()". When the compiler encounters an "Instruction::Call" with a "Value::ForeignFunction" target, it invokes "codegen_call()" in "brillig_call/code_gen_call.rs", which dispatches to "convert_ssa_foreign_call()". Before emitting the foreign call opcode, the compiler must pre-allocate memory for any array results the call will return. This happens through "allocate_external_call_results()", which iterates over the result types. For "Type::Array" results, it delegates to "allocate_foreign_call_result_array()" to recursively allocate memory on the heap for nested arrays. The "BrilligArray" struct is the internal representation of a Noir array in Brillig IR. Its "size" field represents the semi-flattened size, the total number of memory slots the array occupies, accounting for the fact that composite types like tuples consume multiple slots per element. This size is computed by "compute_array_length()" in "brillig_block_variables.rs". For the outer array, "allocate_external_call_results()" correctly uses "define_variable()", which internally calls "allocate_value_with_type()". This function applies the formula above, producing the correct semi-flattened size. However, for nested arrays, "allocate_foreign_call_result_array()" contains a bug. The pattern "Type::Array(_, nested_size)" discards the inner types with "_" and uses only "nested_size", the semantic length of the nested array (the number of logical elements), not the semi-flattened size. For simple element types this works correctly, but for composite element types it under-allocates. Foreign calls returning nested arrays of tuples or other composite types corrupt the Brillig VM heap. Version 1.0.0-beta.19 fixes this issue.