diff --git a/stage0/sema.c b/stage0/sema.c
index 2afa2b29fa..f0286bee1d 100644
--- a/stage0/sema.c
+++ b/stage0/sema.c
@@ -2775,13 +2775,16 @@ static InternPoolIndex resolveEnumDeclFromZir(
             if (tt_inst < zir->inst_len
                 && zir->inst_tags[tt_inst] == ZIR_INST_INT_TYPE) {
                 uint16_t bits = zir->inst_datas[tt_inst].int_type.bit_count;
-                uint8_t signedness
+                // ZIR uses Zig Signedness enum: signed=0, unsigned=1.
+                // IP uses: unsigned=0, signed=1. Invert.
+                uint8_t zir_sign
                     = zir->inst_datas[tt_inst].int_type.signedness;
+                uint8_t ip_sign = (zir_sign == 0) ? 1 : 0;
                 InternPoolKey itk;
                 memset(&itk, 0, sizeof(itk));
                 itk.tag = IP_KEY_INT_TYPE;
                 itk.data.int_type.bits = bits;
-                itk.data.int_type.signedness = signedness;
+                itk.data.int_type.signedness = ip_sign;
                 int_tag_type = ipIntern(s_module_ip, itk);
             }
         }
@@ -3073,6 +3076,28 @@ static void internStringLiteral(const char* str) {
     (void)ipIntern(s_module_ip, bytes2_key);
 }
 
+// --- resolveBuiltinDeclTypes ---
+// Resolve BuiltinDecl types from std.builtin namespace.
+// Ported from Sema.zig analyzeMemoizedState (main stage).
+// This resolves types in BuiltinDecl order: Signedness, AddressSpace,
+// CallingConvention, etc.
+static void resolveBuiltinDeclTypes(uint32_t builtin_ns_idx) {
+    // BuiltinDecl types in order (main stage only).
+    // Each is looked up in std.builtin and resolved.
+    static const char* const builtin_type_names[] = {
+        "Signedness",
+        "AddressSpace",
+    };
+    uint32_t n_types
+        = sizeof(builtin_type_names) / sizeof(builtin_type_names[0]);
+    for (uint32_t i = 0; i < n_types; i++) {
+        uint32_t nav
+            = findNavInNamespace(builtin_ns_idx, builtin_type_names[i]);
+        if (nav != UINT32_MAX)
+            (void)ensureNavValUpToDate(nav);
+    }
+}
+
 // --- resolveStartComptimePreamble ---
 // Create the IP entries that the Zig compiler generates when processing
 // start.zig's comptime block. This block evaluates builtin.zig_backend
@@ -3194,6 +3219,12 @@ static void resolveStartComptimePreamble(void) {
     // start.zig's else branch evaluates @hasDecl(root, "main") which
     // triggers interning of the string literal "main".
     internStringLiteral("main");
+
+    // --- $213+: BuiltinDecl type resolution ---
+    // The Zig compiler calls analyzeMemoizedState which resolves types
+    // from std.builtin in BuiltinDecl order. Port this by resolving each
+    // declaration via ensureNavValUpToDate.
+    resolveBuiltinDeclTypes(builtin_ns_idx);
 }
 
 // --- findDeclImportPathFromZir ---
@@ -9142,13 +9173,16 @@ static void zirUnreachable(Sema* sema, SemaBlock* block, uint32_t inst) {
 // --- zirIntType ---
 // Ported from src/Sema.zig zirIntType.
 static AirInstRef zirIntType(Sema* sema, uint32_t inst) {
-    uint8_t signedness = sema->code.inst_datas[inst].int_type.signedness;
+    // ZIR uses Zig Signedness enum: signed=0, unsigned=1.
+    // IP uses: unsigned=0, signed=1. Invert.
+    uint8_t zir_sign = sema->code.inst_datas[inst].int_type.signedness;
+    uint8_t ip_sign = (zir_sign == 0) ? 1 : 0;
     uint16_t bit_count = sema->code.inst_datas[inst].int_type.bit_count;
     InternPoolKey key;
     memset(&key, 0, sizeof(key));
     key.tag = IP_KEY_INT_TYPE;
     key.data.int_type.bits = bit_count;
-    key.data.int_type.signedness = signedness;
+    key.data.int_type.signedness = ip_sign;
     return AIR_REF_FROM_IP(ipIntern(sema->ip, key));
 }