diff --git a/flang/runtime/extrema.cpp b/flang/runtime/extrema.cpp
--- a/flang/runtime/extrema.cpp
+++ b/flang/runtime/extrema.cpp
@@ -60,7 +60,7 @@
 template <typename COMPARE> class ExtremumLocAccumulator {
 public:
   using Type = typename COMPARE::Type;
-  ExtremumLocAccumulator(const Descriptor &array, std::size_t chars = 0)
+  ExtremumLocAccumulator(const Descriptor &array)
       : array_{array}, argRank_{array.rank()}, compare_{array.ElementBytes()} {
     Reinitialize();
   }
@@ -72,13 +72,21 @@
     previous_ = nullptr;
   }
   int argRank() const { return argRank_; }
-  template <typename A> void GetResult(A *p, int zeroBasedDim = -1) {
+  template <typename A>
+  void GetResult(A *p, int zeroBasedDim = -1, bool scalarFalseMask = false) {
     if (zeroBasedDim >= 0) {
       *p = extremumLoc_[zeroBasedDim] -
           array_.GetDimension(zeroBasedDim).LowerBound() + 1;
     } else {
-      for (int j{0}; j < argRank_; ++j) {
-        p[j] = extremumLoc_[j] - array_.GetDimension(j).LowerBound() + 1;
+      // Either mask is missing or it's scalar .FALSE.
+      if (scalarFalseMask) {
+        // Scalar .FALSE. -- all values are zero
+        *p = 0;
+      } else {
+        // No mask
+        for (int j{0}; j < argRank_; ++j) {
+          p[j] = extremumLoc_[j] - array_.GetDimension(j).LowerBound() + 1;
+        }
       }
     }
   }
@@ -307,7 +315,9 @@
   void Reinitialize() {
     extremum_ = MaxOrMinIdentity<CAT, KIND, IS_MAXVAL>::Value();
   }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = extremum_;
   }
   bool Accumulate(Type x) {
@@ -401,7 +411,9 @@
   explicit CharacterExtremumAccumulator(const Descriptor &array)
       : array_{array}, charLen_{array_.ElementBytes() / KIND} {}
   void Reinitialize() { extremum_ = nullptr; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     static_assert(std::is_same_v<A, Type>);
     if (extremum_) {
       std::memcpy(p, extremum_, charLen_);
@@ -601,7 +613,9 @@
   using AccumType = CppTypeFor<TypeCategory::Real, std::max(KIND, 8)>;
   explicit Norm2Accumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { max_ = sum_ = 0; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     // m * sqrt(1 + sum((others(:)/m)**2))
     *p = static_cast<Type>(max_ * std::sqrt(1 + sum_));
   }
diff --git a/flang/runtime/findloc.cpp b/flang/runtime/findloc.cpp
--- a/flang/runtime/findloc.cpp
+++ b/flang/runtime/findloc.cpp
@@ -94,7 +94,9 @@
       location_[j] = 0;
     }
   }
-  template <typename A> void GetResult(A *p, int zeroBasedDim = -1) {
+  template <typename A>
+  void GetResult(
+      A *p, int zeroBasedDim = -1, bool /*scalarFalseMask*/ = false) {
     if (zeroBasedDim >= 0) {
       *p = location_[zeroBasedDim] -
           array_.GetDimension(zeroBasedDim).LowerBound() + 1;
diff --git a/flang/runtime/product.cpp b/flang/runtime/product.cpp
--- a/flang/runtime/product.cpp
+++ b/flang/runtime/product.cpp
@@ -20,7 +20,9 @@
   explicit NonComplexProductAccumulator(const Descriptor &array)
       : array_{array} {}
   void Reinitialize() { product_ = 1; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = static_cast<A>(product_);
   }
   template <typename A> bool AccumulateAt(const SubscriptValue at[]) {
@@ -37,7 +39,9 @@
 public:
   explicit ComplexProductAccumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { product_ = std::complex<PART>{1, 0}; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     using ResultPart = typename A::value_type;
     *p = {static_cast<ResultPart>(product_.real()),
         static_cast<ResultPart>(product_.imag())};
diff --git a/flang/runtime/reduction-templates.h b/flang/runtime/reduction-templates.h
--- a/flang/runtime/reduction-templates.h
+++ b/flang/runtime/reduction-templates.h
@@ -214,7 +214,8 @@
       // scalar MASK=.FALSE.
       accumulator.Reinitialize();
       for (auto n{result.Elements()}; n-- > 0; result.IncrementSubscripts(at)) {
-        accumulator.GetResult(result.Element<CppType>(at));
+        accumulator.GetResult(result.Element<CppType>(at), /*zeroBasedDim=*/-1,
+            /*scalarFalseMask=*/true);
       }
       return;
     }
diff --git a/flang/runtime/reduction.cpp b/flang/runtime/reduction.cpp
--- a/flang/runtime/reduction.cpp
+++ b/flang/runtime/reduction.cpp
@@ -26,7 +26,9 @@
 public:
   explicit IntegerAndAccumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { and_ = ~INTERMEDIATE{0}; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = static_cast<A>(and_);
   }
   template <typename A> bool AccumulateAt(const SubscriptValue at[]) {
@@ -43,7 +45,9 @@
 public:
   explicit IntegerOrAccumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { or_ = 0; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = static_cast<A>(or_);
   }
   template <typename A> bool AccumulateAt(const SubscriptValue at[]) {
@@ -60,7 +64,9 @@
 public:
   explicit IntegerXorAccumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { xor_ = 0; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = static_cast<A>(xor_);
   }
   template <typename A> bool AccumulateAt(const SubscriptValue at[]) {
diff --git a/flang/runtime/sum.cpp b/flang/runtime/sum.cpp
--- a/flang/runtime/sum.cpp
+++ b/flang/runtime/sum.cpp
@@ -24,7 +24,9 @@
 public:
   explicit IntegerSumAccumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { sum_ = 0; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = static_cast<A>(sum_);
   }
   template <typename A> bool AccumulateAt(const SubscriptValue at[]) {
@@ -42,7 +44,9 @@
   explicit RealSumAccumulator(const Descriptor &array) : array_{array} {}
   void Reinitialize() { sum_ = correction_ = 0; }
   template <typename A> A Result() const { return sum_; }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     *p = Result<A>();
   }
   template <typename A> bool Accumulate(A x) {
@@ -69,7 +73,9 @@
     reals_.Reinitialize();
     imaginaries_.Reinitialize();
   }
-  template <typename A> void GetResult(A *p, int /*zeroBasedDim*/ = -1) const {
+  template <typename A>
+  void GetResult(
+      A *p, int /*zeroBasedDim*/ = -1, bool /*scalarFalseMask*/ = false) const {
     using ResultPart = typename A::value_type;
     *p = {reals_.template Result<ResultPart>(),
         imaginaries_.template Result<ResultPart>()};
diff --git a/flang/unittests/Runtime/Reduction.cpp b/flang/unittests/Runtime/Reduction.cpp
--- a/flang/unittests/Runtime/Reduction.cpp
+++ b/flang/unittests/Runtime/Reduction.cpp
@@ -158,12 +158,84 @@
   EXPECT_EQ(scalarResult.rank(), 0);
   EXPECT_EQ(*scalarResult.ZeroBasedIndexedElement<std::int16_t>(0), 23);
   scalarResult.Destroy();
+
+  // Test .FALSE. scalar MASK argument
+  auto falseMask{MakeArray<TypeCategory::Logical, 4>(
+      std::vector<int>{}, std::vector<std::int32_t>{0})};
+  RTNAME(MaxlocDim)
+  (loc, *array, /*KIND=*/4, /*DIM=*/2, __FILE__, __LINE__,
+      /*MASK=*/&*falseMask, /*BACK=*/false);
+  EXPECT_EQ(loc.rank(), 2);
+  EXPECT_EQ(loc.type().raw(), (TypeCode{TypeCategory::Integer, 4}.raw()));
+  EXPECT_EQ(loc.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(0).Extent(), 3);
+  EXPECT_EQ(loc.GetDimension(1).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(1).Extent(), 2);
+  for (int i{0}; i < 6; ++i) {
+    EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(0), 0);
+  }
+  loc.Destroy();
+
+  // Test .TRUE. scalar MASK argument
+  auto trueMask{MakeArray<TypeCategory::Logical, 4>(
+      std::vector<int>{}, std::vector<std::int32_t>{1})};
+  RTNAME(MaxlocDim)
+  (loc, *array, /*KIND=*/4, /*DIM=*/2, __FILE__, __LINE__,
+      /*MASK=*/&*trueMask, /*BACK=*/false);
+  EXPECT_EQ(loc.rank(), 2);
+  EXPECT_EQ(loc.type().raw(), (TypeCode{TypeCategory::Integer, 4}.raw()));
+  EXPECT_EQ(loc.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(0).Extent(), 3);
+  EXPECT_EQ(loc.GetDimension(1).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(1).Extent(), 2);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(0), 3);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(1), 4);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(2), 3);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(3), 3);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(4), 4);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(5), 4);
+  loc.Destroy();
+
   RTNAME(MinlocDim)
   (scalarResult, *array1, /*KIND=*/2, /*DIM=*/1, __FILE__, __LINE__,
       /*MASK=*/nullptr, /*BACK=*/true);
   EXPECT_EQ(scalarResult.rank(), 0);
   EXPECT_EQ(*scalarResult.ZeroBasedIndexedElement<std::int16_t>(0), 22);
   scalarResult.Destroy();
+
+  // Test .FALSE. scalar MASK argument
+  RTNAME(MinlocDim)
+  (loc, *array, /*KIND=*/4, /*DIM=*/2, __FILE__, __LINE__,
+      /*MASK=*/&*falseMask, /*BACK=*/false);
+  EXPECT_EQ(loc.rank(), 2);
+  EXPECT_EQ(loc.type().raw(), (TypeCode{TypeCategory::Integer, 4}.raw()));
+  EXPECT_EQ(loc.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(0).Extent(), 3);
+  EXPECT_EQ(loc.GetDimension(1).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(1).Extent(), 2);
+  for (int i{0}; i < 6; ++i) {
+    EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(0), 0);
+  }
+  loc.Destroy();
+
+  // Test .TRUE. scalar MASK argument
+  RTNAME(MinlocDim)
+  (loc, *array, /*KIND=*/4, /*DIM=*/2, __FILE__, __LINE__,
+      /*MASK=*/&*trueMask, /*BACK=*/false);
+  EXPECT_EQ(loc.rank(), 2);
+  EXPECT_EQ(loc.type().raw(), (TypeCode{TypeCategory::Integer, 4}.raw()));
+  EXPECT_EQ(loc.GetDimension(0).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(0).Extent(), 3);
+  EXPECT_EQ(loc.GetDimension(1).LowerBound(), 1);
+  EXPECT_EQ(loc.GetDimension(1).Extent(), 2);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(0), 4);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(1), 3);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(2), 4);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(3), 4);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(4), 3);
+  EXPECT_EQ(*loc.ZeroBasedIndexedElement<std::int32_t>(5), 2);
+  loc.Destroy();
+
   RTNAME(MaxvalDim)
   (scalarResult, *array1, /*DIM=*/1, __FILE__, __LINE__, /*MASK=*/nullptr);
   EXPECT_EQ(scalarResult.rank(), 0);