diff --git a/src/ir/type-updating.cpp b/src/ir/type-updating.cpp
index d325e539a9a..3a0f9ea32cb 100644
--- a/src/ir/type-updating.cpp
+++ b/src/ir/type-updating.cpp
@@ -498,7 +498,9 @@ Type GlobalTypeRewriter::getTempTupleType(Tuple tuple) {
 
 namespace TypeUpdating {
 
-void handleNonDefaultableLocals(Function* func, Module& wasm) {
+void handleNonDefaultableLocals(Function* func,
+                                Module& wasm,
+                                Index firstLocal) {
   if (!wasm.features.hasReferenceTypes()) {
     // No references, so no non-nullable ones at all.
     return;
@@ -524,6 +526,9 @@ void handleNonDefaultableLocals(Function* func, Module& wasm) {
     func, wasm, LocalStructuralDominance::NonNullableOnly);
   std::unordered_set<Index> badIndexes;
   for (auto index : info.nonDominatingIndices) {
+    if (index < firstLocal) {
+      continue;
+    }
     badIndexes.insert(index);
 
     // LocalStructuralDominance should have only looked at non-nullable indexes
diff --git a/src/ir/type-updating.h b/src/ir/type-updating.h
index 7aaf02a8234..3db8cbdfba9 100644
--- a/src/ir/type-updating.h
+++ b/src/ir/type-updating.h
@@ -564,7 +564,10 @@ namespace TypeUpdating {
 // them. Atm this turns them into nullable ones, and adds ref.as_non_null on
 // their uses (which keeps the type of the users identical).
 // This may also handle other types of nondefaultable locals in the future.
-void handleNonDefaultableLocals(Function* func, Module& wasm);
+// Ignore locals before firstLocal, if specified.
+void handleNonDefaultableLocals(Function* func,
+                                Module& wasm,
+                                Index firstLocal = 0);
 
 // Returns the type that a local should be, after handling of non-
 // defaultability.
diff --git a/src/parser/parse-5-defs.cpp b/src/parser/parse-5-defs.cpp
index 31048176c42..a3ff8029188 100644
--- a/src/parser/parse-5-defs.cpp
+++ b/src/parser/parse-5-defs.cpp
@@ -16,6 +16,8 @@
 
 #include "wat-parser-internal.h"
 
+#include "ir/type-updating.h"
+
 namespace wasm::WATParser {
 
 Result<> parseDefinitions(
@@ -46,6 +48,7 @@ Result<> parseDefinitions(
     WithPosition with(ctx, decls.funcDefs[i].pos);
     ctx.setSrcLoc(decls.funcDefs[i].annotations);
     ctx.in.setAnnotations(std::move(decls.funcDefs[i].annotations));
+    auto firstScratchLocal = f->getNumLocals();
     if (!f->imported()) {
       CHECK_ERR(ctx.visitFunctionStart(f));
     }
@@ -63,6 +66,8 @@ Result<> parseDefinitions(
       if (auto* err = end.getErr()) {
         return ctx.in.err(decls.funcDefs[i].pos, err->msg);
       }
+      TypeUpdating::handleNonDefaultableLocals(
+        f, decls.wasm, firstScratchLocal);
     }
   }
 
diff --git a/src/wasm/wasm-ir-builder.cpp b/src/wasm/wasm-ir-builder.cpp
index 585a1c98f2a..cd83ea72289 100644
--- a/src/wasm/wasm-ir-builder.cpp
+++ b/src/wasm/wasm-ir-builder.cpp
@@ -2302,7 +2302,7 @@ Result<> IRBuilder::makeBrOn(Index label,
     case BrOnCast:
     case BrOnCastDescEq:
       if (out->isNullable()) {
-        resultType = Type(in->getHeapType(), NonNullable);
+        resultType = in->with(NonNullable);
       } else {
         resultType = *in;
       }
diff --git a/test/lit/basic/br-on-cast-extra-values.wast b/test/lit/basic/br-on-cast-extra-values.wast
new file mode 100644
index 00000000000..6a209939009
--- /dev/null
+++ b/test/lit/basic/br-on-cast-extra-values.wast
@@ -0,0 +1,100 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s -all --roundtrip -S -o - | filecheck %s
+
+(module
+  ;; CHECK:      (type $s (struct))
+  (type $s (struct))
+  ;; CHECK:      (func $extra-values (type $1) (param $s (ref $s)) (result (ref $s) (ref $s))
+  ;; CHECK-NEXT:  (local $scratch (ref $s))
+  ;; CHECK-NEXT:  (local $scratch_3 (ref $s))
+  ;; CHECK-NEXT:  (local $scratch_4 (ref $s))
+  ;; CHECK-NEXT:  (local $scratch_5 (ref $s))
+  ;; CHECK-NEXT:  (local $scratch_2 (ref null $s))
+  ;; CHECK-NEXT:  (block $block1 (type $3) (result (ref $s) (ref $s))
+  ;; CHECK-NEXT:   (local.set $scratch_5
+  ;; CHECK-NEXT:    (block $block (result (ref $s))
+  ;; CHECK-NEXT:     (local.set $scratch_3
+  ;; CHECK-NEXT:      (local.get $s)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (local.set $scratch
+  ;; CHECK-NEXT:      (local.get $s)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (local.set $scratch_2
+  ;; CHECK-NEXT:      (local.get $scratch_3)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (local.set $scratch_4
+  ;; CHECK-NEXT:      (br_on_cast $block (ref $s) (ref $s)
+  ;; CHECK-NEXT:       (local.get $scratch)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (br $block1
+  ;; CHECK-NEXT:      (tuple.make 2
+  ;; CHECK-NEXT:       (ref.as_non_null
+  ;; CHECK-NEXT:        (local.get $scratch_2)
+  ;; CHECK-NEXT:       )
+  ;; CHECK-NEXT:       (local.get $scratch_4)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (tuple.make 2
+  ;; CHECK-NEXT:    (ref.as_non_null
+  ;; CHECK-NEXT:     (local.get $scratch_2)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (local.get $scratch_5)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $extra-values (param $s (ref $s)) (result (ref $s) (ref $s))
+    local.get $s
+    local.get $s
+    br_on_cast 0 (ref $s) (ref $s)
+  )
+  ;; CHECK:      (func $exact (type $2) (param $s (ref (exact $s))) (result (ref (exact $s)) (ref null (exact $s)))
+  ;; CHECK-NEXT:  (local $scratch (ref (exact $s)))
+  ;; CHECK-NEXT:  (local $scratch_3 (ref (exact $s)))
+  ;; CHECK-NEXT:  (local $scratch_4 (ref (exact $s)))
+  ;; CHECK-NEXT:  (local $scratch_2 (ref null (exact $s)))
+  ;; CHECK-NEXT:  (local $scratch_5 (ref null (exact $s)))
+  ;; CHECK-NEXT:  (block $block1 (type $4) (result (ref (exact $s)) (ref null (exact $s)))
+  ;; CHECK-NEXT:   (local.set $scratch_5
+  ;; CHECK-NEXT:    (block $block (result (ref null (exact $s)))
+  ;; CHECK-NEXT:     (local.set $scratch_3
+  ;; CHECK-NEXT:      (local.get $s)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (local.set $scratch
+  ;; CHECK-NEXT:      (local.get $s)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (local.set $scratch_2
+  ;; CHECK-NEXT:      (local.get $scratch_3)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (local.set $scratch_4
+  ;; CHECK-NEXT:      (br_on_cast $block (ref (exact $s)) (ref (exact $s))
+  ;; CHECK-NEXT:       (local.get $scratch)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:     (br $block1
+  ;; CHECK-NEXT:      (tuple.make 2
+  ;; CHECK-NEXT:       (ref.as_non_null
+  ;; CHECK-NEXT:        (local.get $scratch_2)
+  ;; CHECK-NEXT:       )
+  ;; CHECK-NEXT:       (local.get $scratch_4)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (tuple.make 2
+  ;; CHECK-NEXT:    (ref.as_non_null
+  ;; CHECK-NEXT:     (local.get $scratch_2)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (local.get $scratch_5)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $exact (param $s (ref (exact $s)))
+        (result (ref (exact $s)) (ref null (exact $s)))
+    local.get $s
+    local.get $s
+    br_on_cast 0 (ref (exact $s)) (ref null (exact $s))
+  )
+)