diff --git a/src/ir.cpp b/src/ir.cpp
index 616bb23132..5193a63ec4 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -17129,6 +17129,7 @@ static IrInstruction *ir_analyze_instruction_phi(IrAnalyze *ira, IrInstructionPh
     for (size_t i = 0; i < new_incoming_values.length; i += 1) {
         IrInstruction *new_value = new_incoming_values.at(i);
         IrBasicBlock *predecessor = new_incoming_blocks.at(i);
+        ir_assert(predecessor->instruction_list.length != 0, &phi_instruction->base);
         IrInstruction *branch_instruction = predecessor->instruction_list.pop();
         ir_set_cursor_at_end(&ira->new_irb, predecessor);
         IrInstruction *casted_value = ir_implicit_cast(ira, new_value, resolved_type);