diff --git a/astgen.c b/astgen.c
index cac642f070..bd2f14d88e 100644
--- a/astgen.c
+++ b/astgen.c
@@ -5963,8 +5963,7 @@ static void assignOp(
         ext_data.extended.opcode = (uint16_t)ZIR_EXT_INPLACE_ARITH_RESULT_TY;
         ext_data.extended.small = inplace_op;
         ext_data.extended.operand = lhs;
-        rhs_res_ty = addInstruction(gz, ZIR_INST_EXTENDED, ext_data)
-            + ZIR_REF_START_INDEX;
+        rhs_res_ty = addInstruction(gz, ZIR_INST_EXTENDED, ext_data);
     } else {
         rhs_res_ty = addUnNode(gz, ZIR_INST_TYPEOF, lhs, infix_node);
     }
diff --git a/astgen_test.zig b/astgen_test.zig
index 5c8fc6856d..6d61a7dd03 100644
--- a/astgen_test.zig
+++ b/astgen_test.zig
@@ -798,7 +798,7 @@ test "astgen: corpus tokenizer_test.zig" {
 }
 
 test "astgen: corpus astgen_test.zig" {
-    if (true) return error.SkipZigTest; // TODO: store_node ref off-by-1 at inst 1764
+    if (true) return error.SkipZigTest; // TODO: extra data offset mismatches
     const gpa = std.testing.allocator;
     try corpusCheck(gpa, @embedFile("astgen_test.zig"));
 }