diff --git a/flang/lib/Lower/IntrinsicCall.cpp b/flang/lib/Lower/IntrinsicCall.cpp
--- a/flang/lib/Lower/IntrinsicCall.cpp
+++ b/flang/lib/Lower/IntrinsicCall.cpp
@@ -3297,6 +3297,7 @@
                                       llvm::ArrayRef<mlir::Value> args) {
   assert(args.size() == 2);
 
+  mlir::Value zero = builder.createIntegerConstant(loc, resultType, 0);
   mlir::Value ones = builder.createIntegerConstant(loc, resultType, -1);
   mlir::Value bitSize = builder.createIntegerConstant(
       loc, resultType, resultType.getIntOrFloatBitWidth());
@@ -3309,7 +3310,11 @@
   // in this case either, so we choose the most efficient implementation.
   mlir::Value shift =
       builder.create<mlir::arith::SubIOp>(loc, bitSize, bitsToSet);
-  return builder.create<Shift>(loc, ones, shift);
+  mlir::Value shifted = builder.create<Shift>(loc, ones, shift);
+  mlir::Value isZero = builder.create<mlir::arith::CmpIOp>(
+      loc, mlir::arith::CmpIPredicate::eq, bitsToSet, zero);
+
+  return builder.create<mlir::arith::SelectOp>(loc, isZero, zero, shifted);
 }
 
 // MATMUL
diff --git a/flang/test/Lower/Intrinsics/maskl.f90 b/flang/test/Lower/Intrinsics/maskl.f90
--- a/flang/test/Lower/Intrinsics/maskl.f90
+++ b/flang/test/Lower/Intrinsics/maskl.f90
@@ -9,11 +9,14 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskl(a)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i32
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i32
   ! CHECK: %[[BITS:.*]] = arith.constant 32 : i32
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_VAL]] : i32
   ! CHECK: %[[SHIFT:.*]] = arith.shli %[[C__1]], %[[LEN]] : i32
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i32>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_VAL]], %[[C__0]] : i32
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i32
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i32>
 end subroutine maskl_test
 
 ! CHECK-LABEL: maskl1_test
@@ -24,12 +27,15 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskl(a, 1)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i8
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i8
   ! CHECK: %[[BITS:.*]] = arith.constant 8 : i8
   ! CHECK: %[[A_CONV:.*]] = fir.convert %[[A_VAL]] : (i32) -> i8
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_CONV]] : i8
   ! CHECK: %[[SHIFT:.*]] = arith.shli %[[C__1]], %[[LEN]] : i8
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i8>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_CONV]], %[[C__0]] : i8
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i8
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i8>
 end subroutine maskl1_test
 
 ! CHECK-LABEL: maskl2_test
@@ -40,12 +46,15 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskl(a, 2)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i16
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i16
   ! CHECK: %[[BITS:.*]] = arith.constant 16 : i16
   ! CHECK: %[[A_CONV:.*]] = fir.convert %[[A_VAL]] : (i32) -> i16
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_CONV]] : i16
   ! CHECK: %[[SHIFT:.*]] = arith.shli %[[C__1]], %[[LEN]] : i16
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i16>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_CONV]], %[[C__0]] : i16
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i16
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i16>
 end subroutine maskl2_test
 
 ! CHECK-LABEL: maskl4_test
@@ -56,11 +65,14 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskl(a, 4)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i32
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i32
   ! CHECK: %[[BITS:.*]] = arith.constant 32 : i32
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_VAL]] : i32
   ! CHECK: %[[SHIFT:.*]] = arith.shli %[[C__1]], %[[LEN]] : i32
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i32>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_VAL]], %[[C__0]] : i32
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i32
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i32>
 end subroutine maskl4_test
 
 ! CHECK-LABEL: maskl8_test
@@ -71,12 +83,15 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskl(a, 8)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i64
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i64
   ! CHECK: %[[BITS:.*]] = arith.constant 64 : i64
   ! CHECK: %[[A_CONV:.*]] = fir.convert %[[A_VAL]] : (i32) -> i64
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_CONV]] : i64
   ! CHECK: %[[SHIFT:.*]] = arith.shli %[[C__1]], %[[LEN]] : i64
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i64>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_CONV]], %[[C__0]] : i64
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i64
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i64>
 end subroutine maskl8_test
 
 ! TODO: Code containing 128-bit integer literals current breaks. This is
diff --git a/flang/test/Lower/Intrinsics/maskr.f90 b/flang/test/Lower/Intrinsics/maskr.f90
--- a/flang/test/Lower/Intrinsics/maskr.f90
+++ b/flang/test/Lower/Intrinsics/maskr.f90
@@ -9,11 +9,14 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskr(a)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i32
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i32
   ! CHECK: %[[BITS:.*]] = arith.constant 32 : i32
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_VAL]] : i32
   ! CHECK: %[[SHIFT:.*]] = arith.shrui %[[C__1]], %[[LEN]] : i32
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i32>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_VAL]], %[[C__0]] : i32
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i32
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i32>
 end subroutine maskr_test
 
 ! CHECK-LABEL: maskr1_test
@@ -24,12 +27,15 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskr(a, 1)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i8
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i8
   ! CHECK: %[[BITS:.*]] = arith.constant 8 : i8
   ! CHECK: %[[A_CONV:.*]] = fir.convert %[[A_VAL]] : (i32) -> i8
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_CONV]] : i8
   ! CHECK: %[[SHIFT:.*]] = arith.shrui %[[C__1]], %[[LEN]] : i8
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i8>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_CONV]], %[[C__0]] : i8
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i8
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i8>
 end subroutine maskr1_test
 
 ! CHECK-LABEL: maskr2_test
@@ -40,12 +46,15 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskr(a, 2)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i16
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i16
   ! CHECK: %[[BITS:.*]] = arith.constant 16 : i16
   ! CHECK: %[[A_CONV:.*]] = fir.convert %[[A_VAL]] : (i32) -> i16
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_CONV]] : i16
   ! CHECK: %[[SHIFT:.*]] = arith.shrui %[[C__1]], %[[LEN]] : i16
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i16>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_CONV]], %[[C__0]] : i16
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i16
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i16>
 end subroutine maskr2_test
 
 ! CHECK-LABEL: maskr4_test
@@ -56,11 +65,14 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskr(a, 4)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i32
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i32
   ! CHECK: %[[BITS:.*]] = arith.constant 32 : i32
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_VAL]] : i32
   ! CHECK: %[[SHIFT:.*]] = arith.shrui %[[C__1]], %[[LEN]] : i32
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i32>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_VAL]], %[[C__0]] : i32
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i32
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i32>
 end subroutine maskr4_test
 
 ! CHECK-LABEL: maskr8_test
@@ -71,12 +83,15 @@
 
   ! CHECK: %[[A_VAL:.*]] = fir.load %[[A]] : !fir.ref<i32>
   b = maskr(a, 8)
+  ! CHECK: %[[C__0:.*]] = arith.constant 0 : i64
   ! CHECK: %[[C__1:.*]] = arith.constant -1 : i64
   ! CHECK: %[[BITS:.*]] = arith.constant 64 : i64
   ! CHECK: %[[A_CONV:.*]] = fir.convert %[[A_VAL]] : (i32) -> i64
   ! CHECK: %[[LEN:.*]] = arith.subi %[[BITS]], %[[A_CONV]] : i64
   ! CHECK: %[[SHIFT:.*]] = arith.shrui %[[C__1]], %[[LEN]] : i64
-  ! CHECK: fir.store %[[SHIFT]] to %[[B]] : !fir.ref<i64>
+  ! CHECK: %[[IS0:.*]] = arith.cmpi eq, %[[A_CONV]], %[[C__0]] : i64
+  ! CHECK: %[[RESULT:.*]] = arith.select %[[IS0]], %[[C__0]], %[[SHIFT]] : i64
+  ! CHECK: fir.store %[[RESULT]] to %[[B]] : !fir.ref<i64>
 end subroutine maskr8_test
 
 ! TODO: Code containing 128-bit integer literals current breaks. This is