Index: llvm/trunk/lib/Support/APFloat.cpp
===================================================================
--- llvm/trunk/lib/Support/APFloat.cpp
+++ llvm/trunk/lib/Support/APFloat.cpp
@@ -1743,6 +1743,7 @@
 IEEEFloat::opStatus IEEEFloat::mod(const IEEEFloat &rhs) {
   opStatus fs;
   fs = modSpecials(rhs);
+  unsigned int origSign = sign;
 
   while (isFiniteNonZero() && rhs.isFiniteNonZero() &&
          compareAbsoluteValue(rhs) != cmpLessThan) {
@@ -1754,6 +1755,8 @@
     fs = subtract(V, rmNearestTiesToEven);
     assert(fs==opOK);
   }
+  if (isZero())
+    sign = origSign; // fmod requires this
   return fs;
 }
 
Index: llvm/trunk/unittests/ADT/APFloatTest.cpp
===================================================================
--- llvm/trunk/unittests/ADT/APFloatTest.cpp
+++ llvm/trunk/unittests/ADT/APFloatTest.cpp
@@ -3289,6 +3289,20 @@
     EXPECT_EQ(f1.mod(f2), APFloat::opInvalidOp);
     EXPECT_TRUE(f1.isNaN());
   }
+  {
+    APFloat f1(APFloat::IEEEdouble(), "-4.0");
+    APFloat f2(APFloat::IEEEdouble(), "-2.0");
+    APFloat expected(APFloat::IEEEdouble(), "-0.0");
+    EXPECT_EQ(f1.mod(f2), APFloat::opOK);
+    EXPECT_TRUE(f1.bitwiseIsEqual(expected));
+  }
+  {
+    APFloat f1(APFloat::IEEEdouble(), "-4.0");
+    APFloat f2(APFloat::IEEEdouble(), "2.0");
+    APFloat expected(APFloat::IEEEdouble(), "-0.0");
+    EXPECT_EQ(f1.mod(f2), APFloat::opOK);
+    EXPECT_TRUE(f1.bitwiseIsEqual(expected));
+  }
 }
 
 TEST(APFloatTest, PPCDoubleDoubleAddSpecial) {