diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -652,6 +652,8 @@
   (`#63169 <https://github.com/llvm/llvm-project/issues/63169>_`)
 - Fix crash when casting an object to an array type.
   (`#63758 <https://github.com/llvm/llvm-project/issues/63758>_`)
+- Fixed `static_cast` to array of unknown bound.
+  (`#62863 <https://github.com/llvm/llvm-project/issues/62863>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -8853,6 +8853,18 @@
       }
     }
   }
+  if (isa<ExplicitCastExpr>(E)) {
+    QualType DestType = E->getType();
+    if (const auto *IAT = Context.getAsIncompleteArrayType(DestType)) {
+      // C++20 [expr.static.cast]p.4: ... If T is “array of unknown bound of U”,
+      // this direct-initialization defines the type of the expression as U[1]
+      QualType ResultType = Context.getConstantArrayType(
+          IAT->getElementType(),
+          llvm::APInt(Context.getTypeSize(Context.getSizeType()), 1),
+          /*SizeExpr=*/nullptr, ArrayType::Normal, /*IndexTypeQuals=*/0);
+      E->setType(ResultType);
+    }
+  }
 }
 
 QualType Sema::getCompletedType(Expr *E) {
diff --git a/clang/test/SemaCXX/paren-list-agg-init.cpp b/clang/test/SemaCXX/paren-list-agg-init.cpp
--- a/clang/test/SemaCXX/paren-list-agg-init.cpp
+++ b/clang/test/SemaCXX/paren-list-agg-init.cpp
@@ -310,3 +310,23 @@
   constexpr S s(0); // beforecxx20-warning {{aggregate initialization of type 'const S' from a parenthesized list of values is a C++20 extension}} \
                     // expected-error {{constexpr variable 's' must be initialized by a constant expression}}
 }
+
+namespace gh62863 {
+int (&&arr)[] = static_cast<int[]>(42);
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[1]' from a parenthesized list of values is a C++20 extension}}
+int (&&arr1)[1] = static_cast<int[]>(42);
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[1]' from a parenthesized list of values is a C++20 extension}}
+int (&&arr2)[2] = static_cast<int[]>(42); // expected-error {{reference to type 'int[2]' could not bind to an rvalue of type 'int[1]'}}
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[1]' from a parenthesized list of values is a C++20 extension}}
+int (&&arr3)[3] = static_cast<int[3]>(42);
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[3]' from a parenthesized list of values is a C++20 extension}}
+
+int (&&arr4)[] = (int[])(42);
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[1]' from a parenthesized list of values is a C++20 extension}}
+int (&&arr5)[1] = (int[])(42);
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[1]' from a parenthesized list of values is a C++20 extension}}
+int (&&arr6)[2] = (int[])(42); // expected-error {{reference to type 'int[2]' could not bind to an rvalue of type 'int[1]'}}
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[1]' from a parenthesized list of values is a C++20 extension}}
+int (&&arr7)[3] = (int[3])(42);
+// beforecxx20-warning@-1 {{aggregate initialization of type 'int[3]' from a parenthesized list of values is a C++20 extension}}
+}