diff --git a/src/Sema.zig b/src/Sema.zig
index f79f29dc0cc5987d97fe2d1542211262a2883fa6..5827f22dd4678e1658f42458f64d77a8f799b3d7 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -30719,6 +30719,8 @@ fn bitCast(
     }
 
     if (try sema.resolveValue(inst)) |val| {
+        if (val.isUndef(mod))
+            return mod.undefRef(dest_ty);
         if (try sema.bitCastVal(block, inst_src, val, old_ty, dest_ty, 0)) |result_val| {
             return Air.internedToRef(result_val.toIntern());
         }