diff --git a/include/llvm/ADT/APFloat.h b/include/llvm/ADT/APFloat.h
index 3d4a632e531..7e71dd33931 100644
--- a/include/llvm/ADT/APFloat.h
+++ b/include/llvm/ADT/APFloat.h
@@ -510,6 +510,7 @@ private:
   /// \name Miscellany
   /// @{
 
+  bool convertFromStringSpecials(StringRef str);
   opStatus normalize(roundingMode, lostFraction);
   opStatus addOrSubtract(const APFloat &, roundingMode, bool subtract);
   cmpResult compareAbsoluteValue(const APFloat &) const;
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index ec50064f42f..4179231f135 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -2575,11 +2575,40 @@ APFloat::convertFromDecimalString(StringRef str, roundingMode rounding_mode)
   return fs;
 }
 
+bool
+APFloat::convertFromStringSpecials(StringRef str) {
+  if (str.equals("inf") || str.equals("INFINITY")) {
+    makeInf(false);
+    return true;
+  }
+
+  if (str.equals("-inf") || str.equals("-INFINITY")) {
+    makeInf(true);
+    return true;
+  }
+
+  if (str.equals("nan") || str.equals("NaN")) {
+    makeNaN(false, false);
+    return true;
+  }
+
+  if (str.equals("-nan") || str.equals("-NaN")) {
+    makeNaN(false, true);
+    return true;
+  }
+
+  return false;
+}
+
 APFloat::opStatus
 APFloat::convertFromString(StringRef str, roundingMode rounding_mode)
 {
   assert(!str.empty() && "Invalid string length");
 
+  // Handle special cases.
+  if (convertFromStringSpecials(str))
+    return opOK;
+
   /* Handle a leading minus sign.  */
   StringRef::iterator p = str.begin();
   size_t slen = str.size();