diff --git a/stage0/sema.c b/stage0/sema.c
index 451b6307d5..4c22f1295b 100644
--- a/stage0/sema.c
+++ b/stage0/sema.c
@@ -10321,7 +10321,7 @@ static void analyzeMemoizedStateC(void) {
     // not Type and its children (15-35) which are resolved lazily.
     // Among 0-14, only resolve the ones that actually produce entries
     // matching the upstream output.
-    int memoized_limit = 6; // Signedness through SourceLocation
+    int memoized_limit = 3; // Signedness, AddressSpace, CallingConvention
     for (int i = 0; i < memoized_limit; i++) {
         const BuiltinDeclEntry* entry = &s_builtin_decl_entries[i];
 
@@ -12386,16 +12386,20 @@ SemaFuncAirList semaAnalyze(Sema* sema) {
             sema->file_idx = root_file_idx;
             (void)createFileRootStructC(root_file_idx, &sema->code);
 
-            // Evaluate start.zig's comptime blocks. The first block
-            // contains `_ = root;` which resolves @import("root") to
-            // the root module, creating ptr_nav ($136).
+            // Evaluate start.zig's comptime blocks fully, matching the
+            // Zig compiler's ensureComptimeUnitUpToDate. Set
+            // s_in_main_analysis so DECL_VAL resolves declarations
+            // lazily (needed for evaluating switch/if conditions that
+            // access builtin enum values like zig_backend, output_mode).
             if (start_file_idx != UINT32_MAX) {
+                s_in_main_analysis = true;
                 uint32_t start_ns = s_file_namespace[start_file_idx];
                 const SemaNamespace* sns = &s_namespaces[start_ns];
                 for (uint32_t ci = 0; ci < sns->comptime_decl_count; ci++) {
                     analyzeComptimeUnit(
                         start_file_idx, sns->comptime_decls[ci]);
                 }
+                s_in_main_analysis = false;
             }
 
             // Load the builtin module chain by resolving specific
@@ -12425,9 +12429,19 @@ SemaFuncAirList semaAnalyze(Sema* sema) {
                             fi++) {
                             if (s_file_root_type[fi] == bval) {
                                 s_builtin_file_idx = fi;
-                                // Resolve std/builtin.zig's imports
-                                // ($139 std, $140 CG builtin).
-                                resolveModuleDeclImports(fi, 1);
+                                // Resolve std/builtin.zig's "builtin"
+                                // import only (CG builtin module).
+                                // Don't use resolveModuleDeclImports
+                                // which resolves ALL imports including
+                                // "assembly.zig" that the upstream
+                                // doesn't access at this point.
+                                {
+                                    uint32_t bns = s_file_namespace[fi];
+                                    uint32_t bn
+                                        = findNavInNamespace(bns, "builtin");
+                                    if (bn != UINT32_MAX)
+                                        (void)ensureNavValUpToDate(bn);
+                                }
                                 break;
                             }
                         }
@@ -12435,8 +12449,7 @@ SemaFuncAirList semaAnalyze(Sema* sema) {
                 }
             }
 
-            // Trigger memoized state resolution after the full module
-            // chain is loaded.
+            // Trigger memoized state for CallingConvention etc.
             analyzeMemoizedStateC();
 
         } else {