diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -189,6 +189,9 @@
   (`#64876 <https://github.com/llvm/llvm-project/issues/64876>`_)
 - Fixed an assertion if a function has cleanups and fatal erors.
   (`#48974 <https://github.com/llvm/llvm-project/issues/48974>`_)
+- Clang now emits an error if it is not possible to deduce array size for a
+  variable with incomplete array type.
+  (`#37257 <https://github.com/llvm/llvm-project/issues/37257>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -13445,6 +13445,18 @@
     IsParenListInit = !InitSeq.steps().empty() &&
                       InitSeq.step_begin()->Kind ==
                           InitializationSequence::SK_ParenthesizedListInit;
+    QualType VDeclType = VDecl->getType();
+    if (Init && !Init->getType().isNull() &&
+        !Init->getType()->isDependentType() && !VDeclType->isDependentType() &&
+        Context.getAsIncompleteArrayType(VDeclType) &&
+        Context.getAsIncompleteArrayType(Init->getType())) {
+      // Bail out if it is not possible to deduce array size from the
+      // initializer.
+      Diag(VDecl->getLocation(), diag::err_typecheck_decl_incomplete_type)
+          << VDeclType;
+      VDecl->setInvalidDecl();
+      return;
+    }
   }
 
   // Check for self-references within variable initializers.
diff --git a/clang/test/SemaCXX/gh37257.cpp b/clang/test/SemaCXX/gh37257.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/gh37257.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template<class T>
+T&& create();
+
+template<class T, class... Args>
+void test() {
+  T t(create<Args>()...); // expected-error{{variable has incomplete type 'int[]'}}
+  (void) t;
+}
+
+struct A;
+
+int main() {
+  test<int[]>(); // expected-note {{in instantiation of function template specialization 'test<int[]>' requested here}}
+}