diff --git a/src/google/protobuf/arena_align.h b/src/google/protobuf/arena_align.h
index 6b4718e..573caf3 100644
--- a/src/google/protobuf/arena_align.h
+++ b/src/google/protobuf/arena_align.h
@@ -145,7 +145,7 @@
   constexpr size_t Ceil(size_t n) const { return (n + align - 1) & -align; }
   constexpr size_t Floor(size_t n) const { return (n & ~(align - 1)); }
 
-  size_t Padded(size_t n) const {
+  constexpr size_t Padded(size_t n) const {
     // TODO(mvels): there are direct callers of AllocateAligned() that violate
     // `size` being a multiple of `align`: that should be an error / assert.
     //  ABSL_ASSERT(IsAligned(n));