diff --git a/stage0/astgen.c b/stage0/astgen.c
index fcf5245762..72a473ad3d 100644
--- a/stage0/astgen.c
+++ b/stage0/astgen.c
@@ -5866,6 +5866,8 @@ static uint32_t exprRl(GenZir* gz, Scope* scope, ResultLoc rl, uint32_t node) {
         const Ast* stree = ag->tree;
         uint32_t start_node = stree->extra_data.arr[nd.rhs];
         uint32_t end_node = stree->extra_data.arr[nd.rhs + 1];
+        if (end_node == UINT32_MAX)
+            end_node = 0; // OPT() sentinel
         uint32_t sentinel_node = stree->extra_data.arr[nd.rhs + 2];
         // slice_length optimization (AstGen.zig:887-906).
         if (end_node != 0 && stree->nodes.tags[nd.lhs] == AST_NODE_SLICE_OPEN
@@ -14258,6 +14260,8 @@ static bool rlExpr(
         } else if (tag == AST_NODE_LOCAL_VAR_DECL
             || tag == AST_NODE_GLOBAL_VAR_DECL) {
             type_node = tree->extra_data.arr[nd.lhs];
+            if (type_node == UINT32_MAX)
+                type_node = 0; // OPT() sentinel
             init_node = nd.rhs;
         } else { // ALIGNED_VAR_DECL
             init_node = nd.rhs;
@@ -14498,6 +14502,8 @@ static bool rlExpr(
             body_node = tree->extra_data.arr[nd.rhs + 1];
         } else {
             cont_node = tree->extra_data.arr[nd.rhs];
+            if (cont_node == UINT32_MAX)
+                cont_node = 0; // OPT() sentinel
             body_node = tree->extra_data.arr[nd.rhs + 1];
             else_node = tree->extra_data.arr[nd.rhs + 2];
         }
@@ -14635,7 +14641,7 @@ static bool rlExpr(
         ss.end = tree->extra_data.arr[nd.rhs + 1];
         ss.sentinel = tree->extra_data.arr[nd.rhs + 2];
         (void)rlExpr(ag, ss.start, block, RL_RI_TYPE_ONLY);
-        if (ss.end != 0)
+        if (ss.end != UINT32_MAX)
             (void)rlExpr(ag, ss.end, block, RL_RI_TYPE_ONLY);
         (void)rlExpr(ag, ss.sentinel, block, RL_RI_NONE);
         return false;
@@ -15047,16 +15053,16 @@ static bool rlExpr(
                 fp.addrspace_expr = tree->extra_data.arr[pnd.lhs + 2];
                 fp.section_expr = tree->extra_data.arr[pnd.lhs + 3];
                 fp.callconv_expr = tree->extra_data.arr[pnd.lhs + 4];
-                if (fp.param != 0)
+                if (fp.param != UINT32_MAX)
                     (void)rlExpr(ag, fp.param, block, RL_RI_TYPE_ONLY);
-                if (fp.align_expr != 0)
+                if (fp.align_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.align_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.addrspace_expr != 0)
+                if (fp.addrspace_expr != UINT32_MAX)
                     (void)rlExpr(
                         ag, fp.addrspace_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.section_expr != 0)
+                if (fp.section_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.section_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.callconv_expr != 0)
+                if (fp.callconv_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.callconv_expr, block, RL_RI_TYPE_ONLY);
             } else if (ptag == AST_NODE_FN_PROTO) {
                 return_type = pnd.rhs;
@@ -15070,14 +15076,14 @@ static bool rlExpr(
                 for (uint32_t i = fp.params_start; i < fp.params_end; i++)
                     (void)rlExpr(
                         ag, tree->extra_data.arr[i], block, RL_RI_TYPE_ONLY);
-                if (fp.align_expr != 0)
+                if (fp.align_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.align_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.addrspace_expr != 0)
+                if (fp.addrspace_expr != UINT32_MAX)
                     (void)rlExpr(
                         ag, fp.addrspace_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.section_expr != 0)
+                if (fp.section_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.section_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.callconv_expr != 0)
+                if (fp.callconv_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.callconv_expr, block, RL_RI_TYPE_ONLY);
             }
         } else {
@@ -15101,16 +15107,16 @@ static bool rlExpr(
                 fp.addrspace_expr = tree->extra_data.arr[nd.lhs + 2];
                 fp.section_expr = tree->extra_data.arr[nd.lhs + 3];
                 fp.callconv_expr = tree->extra_data.arr[nd.lhs + 4];
-                if (fp.param != 0)
+                if (fp.param != UINT32_MAX)
                     (void)rlExpr(ag, fp.param, block, RL_RI_TYPE_ONLY);
-                if (fp.align_expr != 0)
+                if (fp.align_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.align_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.addrspace_expr != 0)
+                if (fp.addrspace_expr != UINT32_MAX)
                     (void)rlExpr(
                         ag, fp.addrspace_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.section_expr != 0)
+                if (fp.section_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.section_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.callconv_expr != 0)
+                if (fp.callconv_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.callconv_expr, block, RL_RI_TYPE_ONLY);
             } else if (tag == AST_NODE_FN_PROTO) {
                 return_type = nd.rhs;
@@ -15124,14 +15130,14 @@ static bool rlExpr(
                 for (uint32_t i = fp.params_start; i < fp.params_end; i++)
                     (void)rlExpr(
                         ag, tree->extra_data.arr[i], block, RL_RI_TYPE_ONLY);
-                if (fp.align_expr != 0)
+                if (fp.align_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.align_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.addrspace_expr != 0)
+                if (fp.addrspace_expr != UINT32_MAX)
                     (void)rlExpr(
                         ag, fp.addrspace_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.section_expr != 0)
+                if (fp.section_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.section_expr, block, RL_RI_TYPE_ONLY);
-                if (fp.callconv_expr != 0)
+                if (fp.callconv_expr != UINT32_MAX)
                     (void)rlExpr(ag, fp.callconv_expr, block, RL_RI_TYPE_ONLY);
             }
         }
diff --git a/stage0/astgen_test.zig b/stage0/astgen_test.zig
index c539c3de54..c1ea2154fd 100644
--- a/stage0/astgen_test.zig
+++ b/stage0/astgen_test.zig
@@ -286,7 +286,7 @@ fn expectEqualZir(gpa: Allocator, ref: Zir, got: c.Zir) !void {
         for (0..265) |t| {
             if (ref_counts[t] != got_counts[t])
                 std.debug.print("tag {d}: ref={d} got={d} (diff={d})\n", .{
-                    t, ref_counts[t], got_counts[t],
+                    t,                                                                     ref_counts[t], got_counts[t],
                     @as(i32, @intCast(got_counts[t])) - @as(i32, @intCast(ref_counts[t])),
                 });
         }
@@ -787,6 +787,27 @@ const corpus_files = .{
     .{ "parser_test.zig", @embedFile("parser_test.zig") },
     .{ "test_all.zig", @embedFile("test_all.zig") },
     .{ "tokenizer_test.zig", @embedFile("tokenizer_test.zig") },
+
+    .{ "optional.zig", @embedFile("../test/behavior/optional.zig") },
+    .{ "call.zig", @embedFile("../test/behavior/call.zig") },
+    .{ "pointers.zig", @embedFile("../test/behavior/pointers.zig") },
+    .{ "type.zig", @embedFile("../test/behavior/type.zig") },
+    .{ "enum.zig", @embedFile("../test/behavior/enum.zig") },
+    .{ "switch_on_captured_error.zig", @embedFile("../test/behavior/switch_on_captured_error.zig") },
+    .{ "error.zig", @embedFile("../test/behavior/error.zig") },
+    .{ "switch.zig", @embedFile("../test/behavior/switch.zig") },
+    .{ "array.zig", @embedFile("../test/behavior/array.zig") },
+    .{ "slice.zig", @embedFile("../test/behavior/slice.zig") },
+    .{ "basic.zig", @embedFile("../test/behavior/basic.zig") },
+    .{ "packed-struct.zig", @embedFile("../test/behavior/packed-struct.zig") },
+    .{ "eval.zig", @embedFile("../test/behavior/eval.zig") },
+    .{ "field_parent_ptr.zig", @embedFile("../test/behavior/field_parent_ptr.zig") },
+    .{ "struct.zig", @embedFile("../test/behavior/struct.zig") },
+    .{ "floatop.zig", @embedFile("../test/behavior/floatop.zig") },
+    .{ "union.zig", @embedFile("../test/behavior/union.zig") },
+    .{ "math.zig", @embedFile("../test/behavior/math.zig") },
+    .{ "vector.zig", @embedFile("../test/behavior/vector.zig") },
+    .{ "cast.zig", @embedFile("../test/behavior/cast.zig") },
 };
 
 fn corpusCheck(gpa: Allocator, source: [:0]const u8) !void {
@@ -941,11 +962,12 @@ test "astgen: corpus multi_array_list.zig" {
     try corpusCheck(gpa, @embedFile("../lib/std/multi_array_list.zig"));
 }
 
-test "astgen: corpus Sema.zig" {
-    if (true) return error.SkipZigTest; // TODO: too large, work on smaller files first
-    const gpa = std.testing.allocator;
-    try corpusCheck(gpa, @embedFile("../src/Sema.zig"));
-}
+// Later much later
+//test "astgen: corpus Sema.zig" {
+//    if (true) return error.SkipZigTest; // TODO: too large, work on smaller files first
+//    const gpa = std.testing.allocator;
+//    try corpusCheck(gpa, @embedFile("../src/Sema.zig"));
+//}
 
 test "astgen: enum decl" {
     const gpa = std.testing.allocator;
@@ -981,6 +1003,7 @@ test "astgen: corpus" {
     var any_fail = false;
     inline for (corpus_files) |entry| {
         corpusCheck(gpa, entry[1]) catch {
+            std.debug.print("FAIL: {s}\n", .{entry[0]});
             any_fail = true;
         };
     }