diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 295b16c55e2..393ecf4784c 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -1823,7 +1823,7 @@ APFloat::fusedMultiplyAdd(const APFloat &multiplicand,
     /* If two numbers add (exactly) to zero, IEEE 754 decrees it is a
        positive zero unless rounding to minus infinity, except that
        adding two like-signed zeroes gives that zero.  */
-    if (category == fcZero && sign != addend.sign)
+    if (category == fcZero && !(fs & opUnderflow) && sign != addend.sign)
       sign = (rounding_mode == rmTowardNegative);
   } else {
     fs = multiplySpecials(multiplicand);
diff --git a/unittests/ADT/APFloatTest.cpp b/unittests/ADT/APFloatTest.cpp
index c7ec16ba803..8b82fb2f4ed 100644
--- a/unittests/ADT/APFloatTest.cpp
+++ b/unittests/ADT/APFloatTest.cpp
@@ -475,6 +475,47 @@ TEST(APFloatTest, FMA) {
     EXPECT_EQ(12.0f, f1.convertToFloat());
   }
 
+  // Test for correct zero sign when answer is exactly zero.
+  // fma(1.0, -1.0, 1.0) -> +ve 0.
+  {
+    APFloat f1(1.0);
+    APFloat f2(-1.0);
+    APFloat f3(1.0);
+    f1.fusedMultiplyAdd(f2, f3, APFloat::rmNearestTiesToEven);
+    EXPECT_TRUE(!f1.isNegative() && f1.isZero());
+  }
+
+  // Test for correct zero sign when answer is exactly zero and rounding towards
+  // negative.
+  // fma(1.0, -1.0, 1.0) -> +ve 0.
+  {
+    APFloat f1(1.0);
+    APFloat f2(-1.0);
+    APFloat f3(1.0);
+    f1.fusedMultiplyAdd(f2, f3, APFloat::rmTowardNegative);
+    EXPECT_TRUE(f1.isNegative() && f1.isZero());
+  }
+
+  // Test for correct (in this case -ve) sign when adding like signed zeros.
+  // Test fma(0.0, -0.0, -0.0) -> -ve 0.
+  {
+    APFloat f1(0.0);
+    APFloat f2(-0.0);
+    APFloat f3(-0.0);
+    f1.fusedMultiplyAdd(f2, f3, APFloat::rmNearestTiesToEven);
+    EXPECT_TRUE(f1.isNegative() && f1.isZero());
+  }
+
+  // Test -ve sign preservation when small negative results underflow.
+  {
+    APFloat f1(APFloat::IEEEdouble,  "-0x1p-1074");
+    APFloat f2(APFloat::IEEEdouble, "+0x1p-1074");
+    APFloat f3(0.0);
+    f1.fusedMultiplyAdd(f2, f3, APFloat::rmNearestTiesToEven);
+    EXPECT_TRUE(f1.isNegative() && f1.isZero());
+  }
+
+  // Test x87 extended precision case from http://llvm.org/PR20728.
   {
     APFloat M1(APFloat::x87DoubleExtended, 1.0);
     APFloat M2(APFloat::x87DoubleExtended, 1.0);