diff --git a/include/llvm/CodeGen/SDNodeOrdering.h b/include/llvm/CodeGen/SDNodeOrdering.h
index 07dd1a776f2..264753b6510 100644
--- a/include/llvm/CodeGen/SDNodeOrdering.h
+++ b/include/llvm/CodeGen/SDNodeOrdering.h
@@ -18,6 +18,8 @@
 
 namespace llvm {
 
+class SDNode;
+
 /// SDNodeOrdering - Maps a unique (monotonically increasing) value to each
 /// SDNode that roughly corresponds to the ordering of the original LLVM
 /// instruction. This is used for turning off scheduling, because we'll forgo