diff --git a/lib/Analysis/ReachableCode.cpp b/lib/Analysis/ReachableCode.cpp
index a2f3203..8a96744 100644
--- a/lib/Analysis/ReachableCode.cpp
+++ b/lib/Analysis/ReachableCode.cpp
@@ -132,15 +132,21 @@
   // so that we can refine it later.
   SourceLocation L = S->getLocStart();
   if (L.isMacroID()) {
+    SourceManager &SM = PP.getSourceManager();
     if (IgnoreYES_NO) {
       // The Objective-C constant 'YES' and 'NO'
       // are defined as macros.  Do not treat them
       // as configuration values.
-      SourceManager &SM = PP.getSourceManager();
       SourceLocation TopL = getTopMostMacro(L, SM);
       StringRef MacroName = PP.getImmediateMacroName(TopL);
       if (MacroName == "YES" || MacroName == "NO")
         return false;
+    } else if (!PP.getLangOpts().CPlusPlus) {
+      // Do not treat C 'false' and 'true' macros as configuration values.
+      SourceLocation TopL = getTopMostMacro(L, SM);
+      StringRef MacroName = PP.getImmediateMacroName(TopL);
+      if (MacroName == "false" || MacroName == "true")
+        return false;
     }
     return true;
   }
diff --git a/test/Sema/warn-unreachable.c b/test/Sema/warn-unreachable.c
index 34e0296..1f79216 100644
--- a/test/Sema/warn-unreachable.c
+++ b/test/Sema/warn-unreachable.c
@@ -451,3 +451,13 @@
             // CHECK: fix-it:"{{.*}}":{[[@LINE-2]]:15-[[@LINE-2]]:15}:")"
   unaryOpFixitCastSubExpr(x); // expected-warning {{code will never be executed}}
 }
+
+#define false 0
+#define true 1
+
+void testTrueFalseMacros() {
+  if (false) // expected-note {{silence by adding parentheses to mark code as explicitly dead}}
+    testTrueFalseMacros(); // expected-warning {{code will never be executed}}
+  if (!true) // expected-note {{silence by adding parentheses to mark code as explicitly dead}}
+    testTrueFalseMacros(); // expected-warning {{code will never be executed}}
+}