diff --git a/mfbt/Maybe.h b/mfbt/Maybe.h
index 4d26f7af9111..0bf6757c27c2 100644
--- a/mfbt/Maybe.h
+++ b/mfbt/Maybe.h
@@ -265,6 +265,11 @@ struct MaybeStorage<T, false> {
   explicit MaybeStorage(const T& aVal) : mStorage{aVal}, mIsSome{true} {}
   explicit MaybeStorage(T&& aVal) : mStorage{std::move(aVal)}, mIsSome{true} {}
 
+  template <typename... Args>
+  explicit MaybeStorage(Args&&... aArgs) : mIsSome{true} {
+    ::new (KnownNotNull, &mStorage.val) T(std::forward<Args>(aArgs)...);
+  }
+
   // Copy and move operations are no-ops, since copying is moving is implemented
   // by Maybe_CopyMove_Enabler.
 
@@ -299,6 +304,14 @@ struct MaybeStorage<T, true> {
       : mStorage{aVal}, mIsSome{true} {}
   constexpr explicit MaybeStorage(T&& aVal)
       : mStorage{std::move(aVal)}, mIsSome{true} {}
+
+  // XXX This should be constexpr, but then we can't use placement new.
+  // Delegating this to a Union constructor with the same signature doesn't
+  // build out of the box.
+  template <typename... Args>
+  explicit MaybeStorage(Args&&... aArgs) : mIsSome{true} {
+    ::new (KnownNotNull, &mStorage.val) T(std::forward<Args>(aArgs)...);
+  }
 };
 
 }  // namespace detail
@@ -350,9 +363,6 @@ constexpr Maybe<U> Some(T&& aValue);
  * Boost. The most important differences between Maybe and std::optional are:
  *
  *   - std::optional<T> may be compared with T. We deliberately forbid that.
- *   - std::optional allows in-place construction without a separate call to
- *     |emplace()| by using a dummy |in_place_t| value to tag the appropriate
- *     constructor.
  *   - std::optional has |valueOr()|, equivalent to Maybe's |valueOr()|, but
  *     lacks corresponding methods for |refOr()| and |ptrOr()|.
  *   - std::optional lacks |map()| and |apply()|, making it less suitable for
@@ -389,6 +399,10 @@ class MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS Maybe
 
   MOZ_ALLOW_TEMPORARY MOZ_IMPLICIT constexpr Maybe(Nothing) : Maybe{} {}
 
+  template <typename... Args>
+  constexpr explicit Maybe(std::in_place_t, Args&&... aArgs)
+      : detail::MaybeStorage<T>(std::forward<Args>(aArgs)...) {}
+
   /**
    * Maybe<T> can be copy-constructed from a Maybe<U> if T is constructible from
    * a const U&.
diff --git a/mfbt/tests/TestMaybe.cpp b/mfbt/tests/TestMaybe.cpp
index 42929b1be69c..e9b28177c6b0 100644
--- a/mfbt/tests/TestMaybe.cpp
+++ b/mfbt/tests/TestMaybe.cpp
@@ -156,7 +156,7 @@ struct UncopyableUnmovableValue {
 
   ~UncopyableUnmovableValue() { --sUndestroyedObjects; }
 
-  Status GetStatus() { return mStatus; }
+  Status GetStatus() const { return mStatus; }
 
  private:
   UncopyableUnmovableValue(const UncopyableUnmovableValue& aOther) = delete;
@@ -261,6 +261,14 @@ static bool TestBasicFeatures() {
   mayValue.reset();
   MOZ_RELEASE_ASSERT(!mayValue);
 
+  {
+    // Check that Maybe(std::in_place, T1) calls the correct constructor.
+    const auto mayValueConstructed = Maybe<BasicValue>(std::in_place, 1);
+    MOZ_RELEASE_ASSERT(mayValueConstructed);
+    MOZ_RELEASE_ASSERT(mayValueConstructed->GetStatus() == eWasConstructed);
+    MOZ_RELEASE_ASSERT(mayValueConstructed->GetTag() == 1);
+  }
+
   // Check that Some() and Nothing() work.
   mayValue = Some(BasicValue(2));
   MOZ_RELEASE_ASSERT(mayValue);
@@ -497,6 +505,13 @@ static bool TestCopyAndMove() {
   MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
 
   {  // Check that types that support neither moves or copies work.
+    {
+      const auto mayUncopyableUnmovableValueConstructed =
+          Maybe<UncopyableUnmovableValue>{std::in_place};
+      MOZ_RELEASE_ASSERT(mayUncopyableUnmovableValueConstructed->GetStatus() ==
+                         eWasDefaultConstructed);
+    }
+
     Maybe<UncopyableUnmovableValue> mayUncopyableUnmovableValue;
     mayUncopyableUnmovableValue.emplace();
     MOZ_RELEASE_ASSERT(mayUncopyableUnmovableValue->GetStatus() ==