diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 6bab5eca200..676a8466ac2 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1179,6 +1179,12 @@ llvm::ConstantFoldCall(Function *F,
       return 0;
     }
     
+    if (isa<UndefValue>(Operands[0])) {
+      if (Name.startswith("llvm.bswap"))
+        return Operands[0];
+      return 0;
+    }
+
     return 0;
   }
   
diff --git a/test/Transforms/InstCombine/bswap-fold.ll b/test/Transforms/InstCombine/bswap-fold.ll
index 034c70e400c..a6b30c053eb 100644
--- a/test/Transforms/InstCombine/bswap-fold.ll
+++ b/test/Transforms/InstCombine/bswap-fold.ll
@@ -67,3 +67,9 @@ define i16 @test8(i64 %A) {
   %D = tail call i16 @llvm.bswap.i16(i16 %C) nounwind
   ret i16 %D
 }
+
+; Misc: Fold bswap(undef) to undef.
+define i64 @foo() {
+  %a = call i64 @llvm.bswap.i64(i64 undef)
+  ret i64 %a
+}