@@ -109,6 +109,13 @@ class TestStringArray : public ::testing::Test {
     AssertZeroPadded(*strings_);
   }
 
+  void TestArrayCtors() {
+    // ARROW-8863: ArrayData::null_count set to 0 when no validity bitmap
+    // provided
+    ArrayType arr(length_, offsets_buf_, value_buf_);
+    ASSERT_EQ(arr.data()->null_count, 0);
+  }
+
   void TestTotalValuesLength() {
     auto ty = TypeTraits<T>::type_singleton();
     auto arr = ArrayFromJSON(ty, R"(["a", null, "bbb", "cccc", "ddddd"])");
@@ -293,6 +300,8 @@ TYPED_TEST_SUITE(TestStringArray, StringTypes);
 
 TYPED_TEST(TestStringArray, TestArrayBasics) { this->TestArrayBasics(); }
 
+TYPED_TEST(TestStringArray, TestArrayCtors) { this->TestArrayCtors(); }
+
 TYPED_TEST(TestStringArray, TestType) { this->TestType(); }
 
 TYPED_TEST(TestStringArray, TestListFunctions) { this->TestListFunctions(); }
 
@@ -363,7 +363,7 @@ TEST_F(TestArray, ValidateBuffersPrimitive) {
   array = MakeArray(data);
   ASSERT_RAISES(Invalid, array->Validate());
 
-  // Null buffer absent but null_count > 0
+  // Null buffer absent but null_count > 0.
   data = ArrayData::Make(int64(), 2, {nullptr, data_buffer}, 1);
   array = MakeArray(data);
   ASSERT_RAISES(Invalid, array->Validate());
@@ -410,6 +410,13 @@ TEST(TestNullBuilder, Basics) {
 // ----------------------------------------------------------------------
 // Primitive type tests
 
+TEST(TestPrimitiveArray, CtorNoValidityBitmap) {
+  // ARROW-8863
+  std::shared_ptr<Buffer> data = *AllocateBuffer(40);
+  Int32Array arr(10, data);
+  ASSERT_EQ(arr.data()->null_count, 0);
+}
+
 TEST_F(TestBuilder, TestReserve) {
   UInt8Builder builder(pool_);
 
 
@@ -36,14 +36,24 @@ namespace arrow {
 
 using internal::CountSetBits;
 
+static inline void AdjustNonNullable(std::vector<std::shared_ptr<Buffer>>* buffers,
+                                     int64_t* null_count) {
+  if (buffers->size() > 0) {
+    if (*null_count == 0) {
+      // In case there are no nulls, don't keep an allocated null bitmap around
+      (*buffers)[0] = nullptr;
+    } else if (*null_count == kUnknownNullCount && buffers->at(0) == nullptr) {
+      // Conversely, if no null bitmap is provided, set the null count to 0
+      *null_count = 0;
+    }
+  }
+}
+
 std::shared_ptr<ArrayData> ArrayData::Make(const std::shared_ptr<DataType>& type,
                                            int64_t length,
                                            std::vector<std::shared_ptr<Buffer>> buffers,
                                            int64_t null_count, int64_t offset) {
-  // In case there are no nulls, don't keep an allocated null bitmap around
-  if (buffers.size() > 0 && null_count == 0) {
-    buffers[0] = nullptr;
-  }
+  AdjustNonNullable(&buffers, &null_count);
   return std::make_shared<ArrayData>(type, length, std::move(buffers), null_count,
                                      offset);
 }
@@ -53,10 +63,7 @@ std::shared_ptr<ArrayData> ArrayData::Make(
     std::vector<std::shared_ptr<Buffer>> buffers,
     std::vector<std::shared_ptr<ArrayData>> child_data, int64_t null_count,
     int64_t offset) {
-  // In case there are no nulls, don't keep an allocated null bitmap around
-  if (buffers.size() > 0 && null_count == 0) {
-    buffers[0] = nullptr;
-  }
+  AdjustNonNullable(&buffers, &null_count);
   return std::make_shared<ArrayData>(type, length, std::move(buffers),
                                      std::move(child_data), null_count, offset);
 }
@@ -66,9 +73,7 @@ std::shared_ptr<ArrayData> ArrayData::Make(
     std::vector<std::shared_ptr<Buffer>> buffers,
     std::vector<std::shared_ptr<ArrayData>> child_data,
     std::shared_ptr<ArrayData> dictionary, int64_t null_count, int64_t offset) {
-  if (buffers.size() > 0 && null_count == 0) {
-    buffers[0] = nullptr;
-  }
+  AdjustNonNullable(&buffers, &null_count);
   auto data = std::make_shared<ArrayData>(type, length, std::move(buffers),
                                           std::move(child_data), null_count, offset);
   data->dictionary = std::move(dictionary);