diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
index ecc04a6c9a2be..04389bdf44684 100644
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
@@ -1122,6 +1122,16 @@ struct AllocMemOpConversion : public fir::FIROpConversion<fir::AllocMemOp> {
     for (mlir::Value opnd : adaptor.getOperands())
       size = rewriter.create<mlir::LLVM::MulOp>(
           loc, ity, size, integerCast(loc, rewriter, ity, opnd));
+
+    // As the return value of malloc(0) is implementation defined, allocate one
+    // byte to ensure the allocation status being true. This behavior aligns to
+    // what the runtime has.
+    mlir::Value zero = genConstantIndex(loc, ity, rewriter, 0);
+    mlir::Value one = genConstantIndex(loc, ity, rewriter, 1);
+    mlir::Value cmp = rewriter.create<mlir::LLVM::ICmpOp>(
+        loc, mlir::LLVM::ICmpPredicate::sgt, size, zero);
+    size = rewriter.create<mlir::LLVM::SelectOp>(loc, cmp, size, one);
+
     auto mallocTyWidth = lowerTy().getIndexTypeBitwidth();
     auto mallocTy =
         mlir::IntegerType::get(rewriter.getContext(), mallocTyWidth);
diff --git a/flang/test/Fir/alloc-32.fir b/flang/test/Fir/alloc-32.fir
index 3eefc3225fac7..a3cbf200c24fc 100644
--- a/flang/test/Fir/alloc-32.fir
+++ b/flang/test/Fir/alloc-32.fir
@@ -20,7 +20,9 @@ func.func @allocmem_scalar_nonchar() -> !fir.heap<i32> {
 // CHECK-SAME: i32 %[[len:.*]])
 // CHECK: %[[mul1:.*]] = sext i32 %[[len]] to i64
 // CHECK: %[[mul2:.*]] = mul i64 1, %[[mul1]]
-// CHECK: %[[trunc:.*]] = trunc i64 %[[mul2]] to i32
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[mul2]], 0
+// CHECK: %[[sz:.*]] = select i1 %[[cmp]], i64 %[[mul2]], i64 1
+// CHECK: %[[trunc:.*]] = trunc i64 %[[sz]] to i32
 // CHECK: call ptr @malloc(i32 %[[trunc]])
 func.func @allocmem_scalar_dynchar(%l : i32) -> !fir.heap<!fir.char<1,?>> {
   %1 = fir.allocmem !fir.char<1,?>(%l : i32)
diff --git a/flang/test/Fir/alloc.fir b/flang/test/Fir/alloc.fir
index 5b4930bb9cb34..8da8b828c18b9 100644
--- a/flang/test/Fir/alloc.fir
+++ b/flang/test/Fir/alloc.fir
@@ -87,7 +87,9 @@ func.func @alloca_scalar_dynchar_kind(%l : i32) -> !fir.ref<!fir.char<2,?>> {
 // CHECK-SAME: i32 %[[len:.*]])
 // CHECK: %[[mul1:.*]] = sext i32 %[[len]] to i64
 // CHECK: %[[mul2:.*]] = mul i64 1, %[[mul1]]
-// CHECK: call ptr @malloc(i64 %[[mul2]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[mul2]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[mul2]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_scalar_dynchar(%l : i32) -> !fir.heap<!fir.char<1,?>> {
   %1 = fir.allocmem !fir.char<1,?>(%l : i32)
   return %1 : !fir.heap<!fir.char<1,?>>
@@ -97,7 +99,9 @@ func.func @allocmem_scalar_dynchar(%l : i32) -> !fir.heap<!fir.char<1,?>> {
 // CHECK-SAME: i32 %[[len:.*]])
 // CHECK: %[[mul1:.*]] = sext i32 %[[len]] to i64
 // CHECK: %[[mul2:.*]] = mul i64 2, %[[mul1]]
-// CHECK: call ptr @malloc(i64 %[[mul2]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[mul2]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[mul2]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_scalar_dynchar_kind(%l : i32) -> !fir.heap<!fir.char<2,?>>{
   %1 = fir.allocmem !fir.char<2,?>(%l : i32)
   return %1 : !fir.heap<!fir.char<2,?>>
@@ -152,7 +156,9 @@ func.func @allocmem_array_of_char() -> !fir.heap<!fir.array<3x3x!fir.char<1,10>>
 // CHECK-SAME: i32 %[[len:.*]])
 // CHECK: %[[mul1:.*]] = sext i32 %[[len]] to i64
 // CHECK: %[[mul2:.*]] = mul i64 9, %[[mul1]]
-// CHECK: call ptr @malloc(i64 %[[mul2]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[mul2]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[mul2]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_array_of_dynchar(%l: i32) -> !fir.heap<!fir.array<3x3x!fir.char<1,?>>> {
   %1 = fir.allocmem !fir.array<3x3x!fir.char<1,?>>(%l : i32)
   return %1 : !fir.heap<!fir.array<3x3x!fir.char<1,?>>>
@@ -180,7 +186,9 @@ func.func @alloca_dynarray_of_nonchar2(%e: index) -> !fir.ref<!fir.array<?x?xi32
 // CHECK-LABEL: define ptr @allocmem_dynarray_of_nonchar(
 // CHECK-SAME: i64 %[[extent:.*]])
 // CHECK: %[[prod1:.*]] = mul i64 12, %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[prod1]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[prod1]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[prod1]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_dynarray_of_nonchar(%e: index) -> !fir.heap<!fir.array<3x?xi32>> {
   %1 = fir.allocmem !fir.array<3x?xi32>, %e
   return %1 : !fir.heap<!fir.array<3x?xi32>>
@@ -190,7 +198,9 @@ func.func @allocmem_dynarray_of_nonchar(%e: index) -> !fir.heap<!fir.array<3x?xi
 // CHECK-SAME: i64 %[[extent:.*]])
 // CHECK: %[[prod1:.*]] = mul i64 4, %[[extent]]
 // CHECK: %[[prod2:.*]] = mul i64 %[[prod1]], %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[prod2]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[prod2]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[prod2]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_dynarray_of_nonchar2(%e: index) -> !fir.heap<!fir.array<?x?xi32>> {
   %1 = fir.allocmem !fir.array<?x?xi32>, %e, %e
   return %1 : !fir.heap<!fir.array<?x?xi32>>
@@ -218,7 +228,9 @@ func.func @alloca_dynarray_of_char2(%e : index) -> !fir.ref<!fir.array<?x?x!fir.
 // CHECK-LABEL: define ptr @allocmem_dynarray_of_char(
 // CHECK-SAME: i64 %[[extent:.*]])
 // CHECK: %[[prod1:.*]] = mul i64 60, %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[prod1]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[prod1]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[prod1]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_dynarray_of_char(%e : index) -> !fir.heap<!fir.array<3x?x!fir.char<2,10>>> {
   %1 = fir.allocmem !fir.array<3x?x!fir.char<2,10>>, %e
   return %1 : !fir.heap<!fir.array<3x?x!fir.char<2,10>>>
@@ -228,7 +240,9 @@ func.func @allocmem_dynarray_of_char(%e : index) -> !fir.heap<!fir.array<3x?x!fi
 // CHECK-SAME: i64 %[[extent:.*]])
 // CHECK: %[[prod1:.*]] = mul i64 20, %[[extent]]
 // CHECK: %[[prod2:.*]] = mul i64 %[[prod1]], %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[prod2]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[prod2]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[mul2]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_dynarray_of_char2(%e : index) -> !fir.heap<!fir.array<?x?x!fir.char<2,10>>> {
   %1 = fir.allocmem !fir.array<?x?x!fir.char<2,10>>, %e, %e
   return %1 : !fir.heap<!fir.array<?x?x!fir.char<2,10>>>
@@ -261,7 +275,9 @@ func.func @alloca_dynarray_of_dynchar2(%l: i32, %e : index) -> !fir.ref<!fir.arr
 // CHECK: %[[prod1:.*]] = sext i32 %[[len]] to i64
 // CHECK: %[[prod2:.*]] = mul i64 6, %[[prod1]]
 // CHECK: %[[prod3:.*]] = mul i64 %[[prod2]], %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[prod3]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[prod3]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[prod3]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_dynarray_of_dynchar(%l: i32, %e : index) -> !fir.heap<!fir.array<3x?x!fir.char<2,?>>> {
   %1 = fir.allocmem !fir.array<3x?x!fir.char<2,?>>(%l : i32), %e
   return %1 : !fir.heap<!fir.array<3x?x!fir.char<2,?>>>
@@ -273,7 +289,9 @@ func.func @allocmem_dynarray_of_dynchar(%l: i32, %e : index) -> !fir.heap<!fir.a
 // CHECK: %[[prod1:.*]] = mul i64 2, %[[a]]
 // CHECK: %[[prod2:.*]] = mul i64 %[[prod1]], %[[extent]]
 // CHECK: %[[prod3:.*]] = mul i64 %[[prod2]], %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[prod3]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[prod3]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[prod3]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_dynarray_of_dynchar2(%l: i32, %e : index) -> !fir.heap<!fir.array<?x?x!fir.char<2,?>>> {
   %1 = fir.allocmem !fir.array<?x?x!fir.char<2,?>>(%l : i32), %e, %e
   return %1 : !fir.heap<!fir.array<?x?x!fir.char<2,?>>>
@@ -312,7 +330,9 @@ func.func @alloca_array_with_holes_dynchar(%arg0: index, %arg1: index) -> !fir.r
 // CHECK-SAME: i64 %[[e1:.*]], i64 %[[e2:.*]])
 // CHECK: %[[a:.*]] = mul i64 240, %[[e1]]
 // CHECK: %[[b:.*]] = mul i64 %3, %[[e2]]
-// CHECK: call ptr @malloc(i64 %[[b]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[b]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[b]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_array_with_holes_nonchar(%0 : index, %1 : index) -> !fir.heap<!fir.array<4x?x3x?x5xi32>> {
   %a = fir.allocmem !fir.array<4x?x3x?x5xi32>, %0, %1
   return %a : !fir.heap<!fir.array<4x?x3x?x5xi32>>
@@ -321,7 +341,9 @@ func.func @allocmem_array_with_holes_nonchar(%0 : index, %1 : index) -> !fir.hea
 // CHECK-LABEL: define ptr @allocmem_array_with_holes_char(
 // CHECK-SAME: i64 %[[e:.*]])
 // CHECK: %[[mul:.*]] = mul i64 240, %[[e]]
-// CHECK: call ptr @malloc(i64 %[[mul]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[mul]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[mul]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_array_with_holes_char(%e: index) -> !fir.heap<!fir.array<3x?x4x!fir.char<2,10>>> {
   %1 = fir.allocmem !fir.array<3x?x4x!fir.char<2,10>>, %e
   return %1 : !fir.heap<!fir.array<3x?x4x!fir.char<2,10>>>
@@ -331,7 +353,9 @@ func.func @allocmem_array_with_holes_char(%e: index) -> !fir.heap<!fir.array<3x?
 // CHECK-SAME: i64 %[[len:.*]], i64 %[[extent:.*]])
 // CHECK: %[[a:.*]] = mul i64 24, %[[len]]
 // CHECK: %[[b:.*]] = mul i64 %[[a]], %[[extent]]
-// CHECK: call ptr @malloc(i64 %[[b]])
+// CHECK: %[[cmp:.*]] = icmp sgt i64 %[[b]], 0
+// CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[b]], i64 1
+// CHECK: call ptr @malloc(i64 %[[size]])
 func.func @allocmem_array_with_holes_dynchar(%arg0: index, %arg1: index) -> !fir.heap<!fir.array<3x?x4x!fir.char<2,?>>> {
   %1 = fir.allocmem !fir.array<3x?x4x!fir.char<2,?>>(%arg0 : index), %arg1
   return %1 : !fir.heap<!fir.array<3x?x4x!fir.char<2,?>>>
diff --git a/flang/test/Fir/arrexp.fir b/flang/test/Fir/arrexp.fir
index 6c7f71f6f1f9c..e8ec8ac79e0c2 100644
--- a/flang/test/Fir/arrexp.fir
+++ b/flang/test/Fir/arrexp.fir
@@ -146,7 +146,9 @@ func.func @f6(%arg0: !fir.box<!fir.array<?xf32>>, %arg1: f32) {
   // CHECK: %[[EXT_GEP:.*]] = getelementptr {{.*}} %[[A]], i32 0, i32 7, i64 0, i32 1
   // CHECK: %[[EXTENT:.*]] = load i64, ptr %[[EXT_GEP]]
   // CHECK: %[[SIZE:.*]] = mul i64 4, %[[EXTENT]]
-  // CHECK: %[[MALLOC:.*]] = call ptr @malloc(i64 %[[SIZE]])
+  // CHECK: %[[CMP:.*]] = icmp sgt i64 %[[SIZE]], 0
+  // CHECK: %[[SZ:.*]] = select i1 %[[CMP]], i64 %[[SIZE]], i64 1
+  // CHECK: %[[MALLOC:.*]] = call ptr @malloc(i64 %[[SZ]])
   %1 = fir.slice %c2, %c10, %c1 : (index, index, index) -> !fir.slice<1>
   %2 = fir.array_load %arg0 [%1] : (!fir.box<!fir.array<?xf32>>, !fir.slice<1>) -> !fir.array<?xf32>
   %3 = fir.slice %c1, %c9, %c1 : (index, index, index) -> !fir.slice<1>
diff --git a/flang/test/Fir/convert-to-llvm.fir b/flang/test/Fir/convert-to-llvm.fir
index 0e2bfe48a807d..50a98466f0d4b 100644
--- a/flang/test/Fir/convert-to-llvm.fir
+++ b/flang/test/Fir/convert-to-llvm.fir
@@ -216,10 +216,14 @@ func.func @test_alloc_and_freemem_one() {
 }
 
 // CHECK-LABEL:  llvm.func @test_alloc_and_freemem_one() {
-// CHECK:    %[[N:.*]] = llvm.mlir.constant(4 : i64) : i64
-// CHECK-NEXT:    llvm.call @malloc(%[[N]])
-// CHECK:         llvm.call @free(%{{.*}})
-// CHECK-NEXT:    llvm.return
+// CHECK-DAG:    %[[N:.*]] = llvm.mlir.constant(4 : i64) : i64
+// CHECK-DAG:    %[[ZERO:.*]] = llvm.mlir.constant(0 : i64) : i64
+// CHECK-DAG:    %[[ONE:.*]] = llvm.mlir.constant(1 : i64) : i64
+// CHECK-NEXT:   %[[CMP:.*]] = llvm.icmp "sgt" %[[N]], %[[ZERO]] : i64
+// CHECK-NEXT:   %[[SZ:.*]] = llvm.select %[[CMP]], %[[N]], %[[ONE]] : i1, i64
+// CHECK-NEXT:   llvm.call @malloc(%[[SZ]])
+// CHECK:        llvm.call @free(%{{.*}})
+// CHECK-NEXT:   llvm.return
 
 // -----
 // Verify that fir.allocmem is transformed to a call to malloc
@@ -233,8 +237,12 @@ func.func @test_alloc_and_freemem_several() {
 }
 
 // CHECK-LABEL:  llvm.func @test_alloc_and_freemem_several() {
-// CHECK:      %[[N:.*]] = llvm.mlir.constant(400 : i64) : i64
-// CHECK: [[MALLOC:%.*]] = llvm.call @malloc(%[[N]])
+// CHECK-DAG: %[[N:.*]] = llvm.mlir.constant(400 : i64) : i64
+// CHECK-DAG: %[[ZERO:.*]] = llvm.mlir.constant(0 : i64) : i64
+// CHECK-DAG: %[[ONE:.*]] = llvm.mlir.constant(1 : i64) : i64
+// CHECK-NEXT: %[[CMP:.*]] = llvm.icmp "sgt" %[[N]], %[[ZERO]] : i64
+// CHECK-NEXT: %[[SZ:.*]] = llvm.select %[[CMP]], %[[N]], %[[ONE]] : i1, i64
+// CHECK: [[MALLOC:%.*]] = llvm.call @malloc(%[[SZ]])
 // CHECK:              llvm.call @free([[MALLOC]])
 // CHECK:              llvm.return
 
@@ -250,7 +258,11 @@ func.func @test_with_shape(%ncols: index, %nrows: index) {
 // CHECK:   %[[FOUR:.*]] = llvm.mlir.constant(4 : i64) : i64
 // CHECK:   %[[DIM1_SIZE:.*]] = llvm.mul %[[FOUR]], %[[NCOLS]]  : i64
 // CHECK:   %[[TOTAL_SIZE:.*]] = llvm.mul %[[DIM1_SIZE]], %[[NROWS]]  : i64
-// CHECK:   %[[MEM:.*]] = llvm.call @malloc(%[[TOTAL_SIZE]])
+// CHECK:   %[[ZERO:.*]] = llvm.mlir.constant(0 : i64) : i64
+// CHECK:   %[[ONE:.*]] = llvm.mlir.constant(1 : i64) : i64
+// CHECK:   %[[CMP:.*]] = llvm.icmp "sgt" %[[TOTAL_SIZE]], %[[ZERO]] : i64
+// CHECK:   %[[SZ:.*]] = llvm.select %[[CMP]], %[[TOTAL_SIZE]], %[[ONE]] : i1, i64
+// CHECK:   %[[MEM:.*]] = llvm.call @malloc(%[[SZ]])
 // CHECK:   llvm.call @free(%[[MEM]]) : (!llvm.ptr) -> ()
 // CHECK:   llvm.return
 // CHECK: }
@@ -266,7 +278,11 @@ func.func @test_string_with_shape(%len: index, %nelems: index) {
 // CHECK:   %[[ONE:.*]] = llvm.mlir.constant(1 : i64) : i64
 // CHECK:   %[[LEN_SIZE:.*]] = llvm.mul %[[ONE]], %[[LEN]]  : i64
 // CHECK:   %[[TOTAL_SIZE:.*]] = llvm.mul %[[LEN_SIZE]], %[[NELEMS]]  : i64
-// CHECK:   %[[MEM:.*]] = llvm.call @malloc(%[[TOTAL_SIZE]])
+// CHECK:   %[[ZERO:.*]] = llvm.mlir.constant(0 : i64) : i64
+// CHECK:   %[[ONEA:.*]] = llvm.mlir.constant(1 : i64) : i64
+// CHECK:   %[[CMP:.*]] = llvm.icmp "sgt" %[[TOTAL_SIZE]], %[[ZERO]] : i64
+// CHECK:   %[[SZ:.*]] = llvm.select %[[CMP]], %[[TOTAL_SIZE]], %[[ONEA]] : i1, i64
+// CHECK:   %[[MEM:.*]] = llvm.call @malloc(%[[SZ]])
 // CHECK:   llvm.call @free(%[[MEM]]) : (!llvm.ptr) -> ()
 // CHECK:   llvm.return
 // CHECK: }
diff --git a/flang/test/Lower/forall/character-1.f90 b/flang/test/Lower/forall/character-1.f90
index 1e4bb73350871..d1e12a8dbdfec 100644
--- a/flang/test/Lower/forall/character-1.f90
+++ b/flang/test/Lower/forall/character-1.f90
@@ -29,7 +29,9 @@ end program test
 ! CHECK: %[[esval:.*]] = load i64, ptr %[[elesize]]
 ! CHECK: %[[mul:.*]] = mul i64 1, %[[esval]]
 ! CHECK: %[[mul2:.*]] = mul i64 %[[mul]], %[[extval]]
-! CHECK: %[[buff:.*]] = call ptr @malloc(i64 %[[mul2]])
+! CHECK: %[[cmp:.*]] = icmp sgt i64 %[[mul2]], 0
+! CHECK: %[[size:.*]] = select i1 %[[cmp]], i64 %[[mul2]], i64 1
+! CHECK: %[[buff:.*]] = call ptr @malloc(i64 %[[size]])
 ! CHECK: %[[to:.*]] = getelementptr i8, ptr %[[buff]], i64 %
 ! CHECK: call void @llvm.memmove.p0.p0.i64(ptr %[[to]], ptr %{{.*}}, i64 %{{.*}}, i1 false)
 ! CHECK: call void @free(ptr %[[buff]])