diff --git a/src/stage1/ir.cpp b/src/stage1/ir.cpp
index 7906df3b0..566f5f83f 100644
--- a/src/stage1/ir.cpp
+++ b/src/stage1/ir.cpp
@@ -30687,8 +30687,8 @@ static IrInstGen *ir_analyze_bit_cast(IrAnalyze *ira, IrInst* source_instr, IrIn
     const bool src_is_ptr = handle_is_ptr(ira->codegen, src_type);
     const bool dest_is_ptr = handle_is_ptr(ira->codegen, dest_type);
 
-    const uint64_t dest_size_bytes = type_size(ira->codegen, dest_type);
-    const uint64_t src_size_bytes = type_size(ira->codegen, src_type);
+    const uint64_t dest_size_bytes = type_size_bits(ira->codegen, dest_type);
+    const uint64_t src_size_bytes = type_size_bits(ira->codegen, src_type);
     if (dest_size_bytes != src_size_bytes) {
         ir_add_error(ira, source_instr,
             buf_sprintf("destination type '%s' has size %" ZIG_PRI_u64 " but source type '%s' has size %" ZIG_PRI_u64,