diff --git a/ets2panda/checker/ets/function.cpp b/ets2panda/checker/ets/function.cpp
index adeea4b940ed1d850b018bb20284a82b3b58659c..55f265ba5c9f5eaae71643cd2ef472d3c55b4424 100644
--- a/ets2panda/checker/ets/function.cpp
+++ b/ets2panda/checker/ets/function.cpp
@@ -1317,7 +1317,7 @@ static bool AppendSignatureInfoParam(ETSChecker *checker, SignatureInfo *sigInfo
     if (!param->IsOptional()) {
         ++sigInfo->minArgCount;
     }
-    ES2PANDA_ASSERT(!param->IsOptional() ||
+    ES2PANDA_ASSERT(!param->IsOptional() || param->Ident()->TsType()->IsTypeError() ||
                     checker->Relation()->IsSupertypeOf(param->Ident()->TsType(), checker->GlobalETSUndefinedType()));
     return true;
 }
diff --git a/ets2panda/checker/ets/utilityTypeHandlers.cpp b/ets2panda/checker/ets/utilityTypeHandlers.cpp
index 94f186f970ec6462b47d9b80d7d9d444d7dffb32..256f917fe5b2ffa7b569b102c983b695f42b9b71 100644
--- a/ets2panda/checker/ets/utilityTypeHandlers.cpp
+++ b/ets2panda/checker/ets/utilityTypeHandlers.cpp
@@ -487,6 +487,34 @@ void ETSChecker::CreatePartialClassDeclaration(ir::ClassDefinition *const newCla
     newClassDefinition->Variable()->SetTsType(nullptr);
 }
 
+static void SetupFunctionParams(ir::ScriptFunction *function, varbinder::FunctionParamScope *paramScope,
+                                checker::ETSChecker *checker)
+{
+    for (auto *params : function->Params()) {
+        auto *paramExpr = params->AsETSParameterExpression();
+        if (paramExpr->Ident()->TypeAnnotation() == nullptr) {
+            paramExpr->Ident()->SetTsTypeAnnotation(nullptr);
+        } else {
+            auto *unionType =
+                // SUPPRESS_CSA_NEXTLINE(alpha.core.AllocatorETSCheckerHint)
+                checker->AllocNode<ir::ETSUnionType>(
+                    ArenaVector<ir::TypeNode *>({paramExpr->Ident()->TypeAnnotation(),
+                                                 // SUPPRESS_CSA_NEXTLINE(alpha.core.AllocatorETSCheckerHint)
+                                                 checker->AllocNode<ir::ETSUndefinedType>(checker->Allocator())},
+                                                checker->Allocator()->Adapter()),
+                    checker->Allocator());
+            paramExpr->Ident()->SetTsTypeAnnotation(unionType);
+            unionType->SetParent(paramExpr->Ident());
+        }
+        auto [paramVar, node] = paramScope->AddParamDecl(checker->Allocator(), checker->VarBinder(), paramExpr);
+        if (node != nullptr) {
+            checker->VarBinder()->ThrowRedeclaration(node->Start(), paramVar->Name());
+        }
+
+        paramExpr->SetVariable(paramVar);
+    }
+}
+
 ir::MethodDefinition *ETSChecker::CreateNullishAccessor(ir::MethodDefinition *const accessor,
                                                         ir::TSInterfaceDeclaration *interface)
 {
@@ -531,27 +559,8 @@ ir::MethodDefinition *ETSChecker::CreateNullishAccessor(ir::MethodDefinition *co
                                         Allocator()->Adapter()),
             Allocator()));
     } else {
-        for (auto *params : function->Params()) {
-            auto *paramExpr = params->AsETSParameterExpression();
-
-            auto *unionType =
-                // SUPPRESS_CSA_NEXTLINE(alpha.core.AllocatorETSCheckerHint)
-                AllocNode<ir::ETSUnionType>(
-                    ArenaVector<ir::TypeNode *>({paramExpr->Ident()->TypeAnnotation(),
-                                                 // SUPPRESS_CSA_NEXTLINE(alpha.core.AllocatorETSCheckerHint)
-                                                 AllocNode<ir::ETSUndefinedType>(Allocator())},
-                                                Allocator()->Adapter()),
-                    Allocator());
-            paramExpr->Ident()->SetTsTypeAnnotation(unionType);
-            unionType->SetParent(paramExpr->Ident());
-
-            auto [paramVar, node] = paramScope->AddParamDecl(Allocator(), VarBinder(), paramExpr);
-            if (node != nullptr) {
-                VarBinder()->ThrowRedeclaration(node->Start(), paramVar->Name());
-            }
-
-            paramExpr->SetVariable(paramVar);
-        }
+        // SUPPRESS_CSA_NEXTLINE(alpha.core.AllocatorETSCheckerHint)
+        SetupFunctionParams(function, paramScope, this);
     }
 
     nullishAccessor->SetOverloads(ArenaVector<ir::MethodDefinition *>(Allocator()->Adapter()));
diff --git a/ets2panda/test/ast/compiler/ets/type_error_processing/param_typeannotation_null.ets b/ets2panda/test/ast/compiler/ets/type_error_processing/param_typeannotation_null.ets
new file mode 100644
index 0000000000000000000000000000000000000000..a630a094e64ebcabcb6a12f2a003cb19e54b36cc
--- /dev/null
+++ b/ets2panda/test/ast/compiler/ets/type_error_processing/param_typeannotation_null.ets
@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2025 Huawei Device Co., Ltd.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+interface inter <T>{
+    get value(): Double;
+    set value(A = Int.MAX_VALUE + 1);
+}
+
+function foo(i: Partial<inter<String>>): void {}
+
+/* @@? 18:15 Error TypeError: The type of parameter 'A' cannot be inferred */
+/* @@? 18:15 Error TypeError: The type of parameter 'A' cannot be inferred */
+/* @@? 18:17 Error SyntaxError: Parameter declaration should have an explicit type annotation. */
diff --git a/ets2panda/test/test-lists/astchecker/astchecker-ets-ignored.txt b/ets2panda/test/test-lists/astchecker/astchecker-ets-ignored.txt
index bb991b21cc0e1c7221a26d21a1801bbffd551f58..0f620ba2ca792302ded0e4b9d1eceb1565ce9bd9 100644
--- a/ets2panda/test/test-lists/astchecker/astchecker-ets-ignored.txt
+++ b/ets2panda/test/test-lists/astchecker/astchecker-ets-ignored.txt
@@ -57,6 +57,10 @@ ast/compiler/ets/implicit_this_method_trailing.ets
 ast/parser/ets/import_tests/export_and_import_class.ets
 ast/parser/ets/import_tests/export_and_import_top_level.ets
 
+# This case will emit different error messages on debug and release builds.
+# It behaves different because `Phase::Apply` contains `#ifndef NDEBUG`.
+ast/compiler/ets/type_error_processing/param_typeannotation_null.ets
+
 # Issue: #22951
 ast/compiler/ets/extension_accessor_tests/getterAsFunctionCall.ets
 ast/compiler/ets/extension_accessor_tests/getterAsMethodCall.ets