diff --git a/runtime/bin/ffi_test/ffi_test_functions.cc b/runtime/bin/ffi_test/ffi_test_functions.cc
index 62c349b29a6..d0f4db35905 100644
--- a/runtime/bin/ffi_test/ffi_test_functions.cc
+++ b/runtime/bin/ffi_test/ffi_test_functions.cc
@@ -123,6 +123,14 @@ DART_EXPORT int64_t IntComputation(int8_t a, int16_t b, int32_t c, int64_t d) {
   return retval;
 }
 
+// Used in regress_39044_test.dart.
+DART_EXPORT int64_t Regress39044(int64_t a, int8_t b) {
+  std::cout << "Regress39044(" << a << ", " << static_cast<int>(b) << ")\n";
+  const int64_t retval = a - b;
+  std::cout << "returning " << retval << "\n";
+  return retval;
+}
+
 // Performs some computation on various sized unsigned ints.
 // Used for testing value ranges for unsigned ints.
 DART_EXPORT int64_t UintComputation(uint8_t a,
diff --git a/runtime/vm/compiler/backend/il.cc b/runtime/vm/compiler/backend/il.cc
index b5f807aeb65..981737f240a 100644
--- a/runtime/vm/compiler/backend/il.cc
+++ b/runtime/vm/compiler/backend/il.cc
@@ -1117,7 +1117,8 @@ ConstantInstr::ConstantInstr(const Object& value, TokenPosition token_pos)
 bool ConstantInstr::AttributesEqual(Instruction* other) const {
   ConstantInstr* other_constant = other->AsConstant();
   ASSERT(other_constant != NULL);
-  return (value().raw() == other_constant->value().raw());
+  return (value().raw() == other_constant->value().raw() &&
+          representation() == other_constant->representation());
 }
 
 UnboxedConstantInstr::UnboxedConstantInstr(const Object& value,
diff --git a/tests/ffi/regress_39044_test.dart b/tests/ffi/regress_39044_test.dart
new file mode 100644
index 00000000000..785500dab74
--- /dev/null
+++ b/tests/ffi/regress_39044_test.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// Check that the optimizer does not fuse constants with different
+// representations.
+//
+// SharedObjects=ffi_test_functions
+
+import "dart:ffi";
+
+import "package:expect/expect.dart";
+
+import "dylib_utils.dart";
+
+main() {
+  final ffiTestFunctions = dlopenPlatformSpecific("ffi_test_functions");
+
+  final intComputation = ffiTestFunctions.lookupFunction<
+      Int64 Function(Int64, Int8), int Function(int, int)>("Regress39044");
+
+  // The arguments are the same Smi constant, however they are different sizes.
+  final result = intComputation(
+      /* dart::kUnboxedInt64 --> int64_t             */ 1,
+      /* dart::kUnboxedInt32 --> truncated to int8_t */ 1);
+
+  Expect.equals(0, result);
+}